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Creamy Mushroom Green Bean Casserole with Crispy Onions Recipe

BySarah
Jump to Recipe· 4.8 from 12 reviews

If you’re craving a comfort food classic with a fresh, flavorful twist, I have just the thing for you: Creamy Mushroom Green Bean Casserole with Crispy Onions Recipe. This isn’t your run-of-the-mill green bean casserole; it’s packed with savory cremini mushrooms, a luscious creamy sauce, and that irresistible crunch of crispy onions on top. Trust me, once you try this, it’ll become your go-to side dish for family dinners, holidays, or anytime you want some serious cozy vibes on your plate.

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Why This Recipe Works

  • Balance of textures: Tender green beans paired with creamy mushroom sauce and crispy onions create a perfect harmony of soft and crunchy.
  • Deep umami flavor: Cremini mushrooms sautéed with tamari and garlic build rich layers of savory goodness in every bite.
  • Easy homemade crispy onions: Skip the store-bought ones and bake your own for lighter, fresher crisp toppings.
  • Versatile and approachable: With straightforward ingredients and simple steps, this recipe suits everyday dinners or special occasions alike.
Creamy Mushroom Green Bean Casserole with Crispy Onions, green bean casserole, mushroom side dish, holiday green bean casserole, crispy onion casserole - A white square tray filled with a single thin layer of crispy fried onion strings, showing a mix of pale golden and light brown colors, some pieces are curled and others are straight, with slight dark brown edges indicating toasted spots. The texture looks crunchy and scattered unevenly across the tray, resting on a white marbled surface. Photo taken with an iphone --ar 2:3 --v 7 this …

Ingredients & Why They Work

This Creamy Mushroom Green Bean Casserole with Crispy Onions Recipe comes together from a handful of fresh, accessible ingredients that each bring something special. I always recommend using fresh green beans and mushrooms for the best flavor and texture, plus simple pantry staples to make the sauce creamy and lush.

Creamy Mushroom Green Bean Casserole with Crispy Onions, green bean casserole, mushroom side dish, holiday green bean casserole, crispy onion casserole - Flat lay of fresh green beans trimmed and halved, sliced cremini mushrooms with their smooth, brown caps, whole garlic cloves with papery white skin, sprigs of fresh thyme with tiny green leaves, a wedge of pale yellow Parmesan cheese showing its textured rind, whole yellow onions with golden brown skin, crisp French fried onions with a light golden color and crunchy texture, and a small bowl of creamy milk with a smooth white surface, all beautifully arranged in natural clusters and scattered artfully, placed on white marbled surface, photo taken with an iphone --ar 2:3 --v 7
  • Green beans: Fresh beans give you that snap and vibrant color; blanching them locks in both.
  • Extra-virgin olive oil: A good-quality olive oil adds depth when sautéing mushrooms without overpowering.
  • Cremini mushrooms: Their robust flavor and meaty texture act as the umami powerhouse.
  • Tamari: A gluten-free soy sauce that enhances the mushrooms with a salty, savory note.
  • Garlic cloves: Fresh garlic punches up the aroma and taste, making the sauce irresistible.
  • Fresh thyme leaves: Adds an earthy herbaceous touch that complements mushroom and green beans beautifully.
  • All-purpose flour: For thickening the sauce, a classic step to get that cozy creaminess.
  • Milk: Use whatever kind you prefer; whole milk is rich, but plant-based works great for a lighter or vegan twist.
  • Dijon mustard: Just a hint wakes up the cream sauce with tangy complexity.
  • Parmesan cheese: Provides a salty, nutty finish—skip it for vegan versions or try nutritional yeast.
  • Freshly ground black pepper: For seasoning with a subtle heat that cuts through the creaminess.
  • French fried onions or homemade crispy baked onions: The star crunch topping that brings the dish alive.
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Note: You’ll find the complete list of ingredients, along with their exact measurements, in the printable recipe card at the bottom of this post.

Tweak to Your Taste

I love how adaptable this Creamy Mushroom Green Bean Casserole with Crispy Onions Recipe is. Over time, I’ve found some fun ways to customize it depending on what I have on hand or my mood—so don’t be shy about making it your own!

  • Vegan twist: I swap out the Parmesan for nutritional yeast and use plant-based milk—don’t forget to add a pinch more salt to boost flavor.
  • Extra herbaceous: Try adding sautéed shallots or a sprinkle of fresh rosemary for deeper fragrance.
  • Crispier topping: Homemade crispy baked onions are my favorite—they stay crunchier and taste way fresher than store-bought.
  • More texture: Toss in toasted walnuts or pecans on top if you crave an extra crunch beyond the onions.

Step-by-Step: How I Make Creamy Mushroom Green Bean Casserole with Crispy Onions Recipe

Step 1: Blanch the Green Beans to Keep That Perfect Snap

Start by bringing a large pot of salted water to a boil. While you wait, prepare a big bowl of ice water—this is crucial! Drop your trimmed and halved green beans into the boiling water for exactly 4 minutes. Then, drain and swiftly dunk them into the ice bath to halt cooking immediately. This step locks in the bright green color and keeps your beans tender yet crisp. After a few minutes, drain again and pat dry with a towel. I always pat them as dry as possible to avoid watery casserole.

Step 2: Sauté Mushrooms with Garlic, Thyme, and Tamari for Flavor Magic

Heat 2 tablespoons of extra-virgin olive oil in a large skillet over medium heat. Add your sliced cremini mushrooms and cook for 8 to 10 minutes, stirring occasionally until soft and golden. Now stir in the tamari, minced garlic, and fresh thyme leaves—your kitchen will start smelling incredible. The tamari deepens the umami flavor, while fresh thyme adds that subtle herbal lift.

Step 3: Whisk in Flour, Milk, and Dijon to Build Creamy Sauce

Sprinkle the flour evenly over the mushrooms and stir to coat, cooking for another minute to eliminate any raw flour taste. Slowly pour in your milk while whisking constantly to prevent lumps. Add the Dijon mustard for brightness. Simmer gently, whisking often, for 15 to 20 minutes until the sauce thickens beautifully. Finally, stir in grated Parmesan cheese and freshly ground black pepper to taste. This sauce is my favorite part — it’s rich, silky, and packed with flavor.

Step 4: Assemble, Top with Onions, and Bake to Perfection

Preheat your oven to 400°F and lightly grease a 9×13-inch baking dish. Spread about one-third of the sauce on the bottom of the dish. Add a layer of the blanched green beans, then top with the remaining sauce. Sprinkle 1½ cups of French fried onions or your homemade crispy baked onions on top. Cover the dish with foil and bake for 10 minutes, then remove the foil and bake for another 10 minutes uncovered. If the onions brown too much, cover the dish loosely again to prevent burning. For an extra cheesy finish, sprinkle a little Parmesan on top before serving.

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Pro Tips for Making Creamy Mushroom Green Bean Casserole with Crispy Onions Recipe

  • Perfect blanching: Don’t skip the ice bath — it’s key to vibrant color and crisp texture in your green beans.
  • Homemade crispy onions: Baking your own onions means less oil, lighter crunch, and richer onion flavor without preservatives.
  • Whisk milk in gradually: To avoid lumps in the sauce, add milk a bit at a time while whisking vigorously.
  • Cover when browning too fast: Keep foil handy to shield onions if they darken before the casserole is done baking.

How to Serve Creamy Mushroom Green Bean Casserole with Crispy Onions Recipe

Creamy Mushroom Green Bean Casserole with Crispy Onions, green bean casserole, mushroom side dish, holiday green bean casserole, crispy onion casserole - A rectangular gray casserole dish filled with a layered green bean casserole sits on a white marbled surface with a blue and white striped cloth beneath it. The bottom layer consists of fresh, bright green beans arranged evenly, topped with a thick layer of creamy sauce mixed with the beans, and the top layer shows golden brown, crispy fried onions scattered generously, some darker and some lighter in color creating a textured look. In the background, there is a clear glass of white wine, a bottle, a wooden pepper grinder, and a small bowl of salt, all resting on the same white marbled surface. The dish looks warm and ready to serve. photo taken with an iphone --ar 2:3 --v 7

Garnishes

I love to sprinkle extra Parmesan right after baking for a melty, cheesy finish. Fresh thyme sprigs also add such a pretty rustic look and a little herbal aroma when serving. Sometimes I toss a few toasted sliced almonds on top for extra nutty crunch — it’s unexpected but delicious!

Side Dishes

This casserole pairs beautifully with roasted turkey or chicken for a cozy meal. For vegetarian dinners, I serve it alongside quinoa or wild rice and a fresh green salad. Mashed potatoes or dinner rolls complete the table perfectly, soaking up all that creamy mushroom sauce.

Creative Ways to Present

For special occasions, try serving individual portions in ramekins topped with homemade crispy onions—everyone loves a personal casserole. Or bake it in a shallow ceramic dish and garnish with edible flowers and fresh herbs for a beautiful holiday centerpiece.

Make Ahead and Storage

Storing Leftovers

I store leftover casserole covered tightly in the fridge for up to 3 days. The creamy sauce thickens naturally as it chills, so give it a gentle stir when reheating. Keeping the crispy onions separate until serving helps maintain their crunch.

Freezing

This recipe freezes surprisingly well! I freeze it without the crispy onions on top, in an airtight container. When ready to serve, thaw overnight in the fridge, then add fresh or leftover crispy onions before baking as usual.

Reheating

To reheat, pop your casserole in a 350°F oven covered with foil for about 20 minutes or until warmed through. Uncover in the last 5 minutes to crispen up the onions. If your onions have softened, sprinkle a few fresh crispy onions on top for that perfect finish.

FAQs

  1. Can I use frozen green beans for this casserole?

    Yes, you can! Just thaw them completely and pat dry before adding to the casserole. Keep in mind frozen beans can be a bit softer, so you might want to reduce blanching time or skip blanching altogether to prevent mushiness.

  2. How do I make the crispy onions at home?

    Thinly slice yellow onions and toss them in olive oil, flour, panko breadcrumbs, and salt. Spread them on parchment-lined baking sheets and bake at a high temperature, stirring every 10 minutes until golden and crunchy. It’s lighter and fresher than store-bought versions.

  3. Can I make this casserole vegan?

    Absolutely! Simply omit the Parmesan cheese and substitute plant-based milk. Add a pinch more salt to the sauce to enhance flavor. Using nutritional yeast in place of cheese adds a cheesy note.

  4. Why is my sauce lumpy and how do I fix it?

    Lumps usually happen when milk is added too quickly or flour isn’t fully incorporated. To avoid lumps, whisk continuously while adding milk slowly. If lumps appear, try straining the sauce or whisking it vigorously over gentle heat until smooth.

Final Thoughts

This Creamy Mushroom Green Bean Casserole with Crispy Onions Recipe holds a special place on my table — it’s the kind of dish that brings everyone together with its comforting warmth and satisfying crunch. Whether you’re making it for a holiday feast or a casual weeknight dinner, it never fails to impress. I hope you enjoy making it as much as I do, and maybe even add your own spin along the way. So grab those fresh green beans and mushrooms, and let’s get cooking!

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Creamy Mushroom Green Bean Casserole with Crispy Onions Recipe

5 Stars 4 Stars 3 Stars 2 Stars 1 Star 4.8 from 12 reviews
  • Author: Sarah
  • Prep Time: 20 minutes
  • Cook Time: 1 hour
  • Total Time: 1 hour 20 minutes
  • Yield: 8 servings
  • Category: Side Dish
  • Method: Baking
  • Cuisine: American
  • Diet: Vegetarian
Print Recipe

Description

A classic Green Bean Casserole made with fresh green beans, a savory mushroom sauce enhanced with tamari and fresh thyme, topped with crispy French fried onions and Parmesan cheese. This comforting dish is baked to perfection and perfect for holiday meals or family dinners.

Ingredients

Green Beans and Topping

  • 1½ pounds green beans, trimmed and halved
  • 1½ cups French fried onions, or homemade Crispy Baked Onions (see recipe notes)
  • Extra Parmesan cheese for sprinkling

Mushroom Sauce

  • 2 tablespoons extra-virgin olive oil
  • 16 ounces cremini mushrooms, sliced
  • 2 tablespoons tamari
  • 4 garlic cloves, minced
  • 2 tablespoons fresh thyme leaves
  • ¼ cup all-purpose flour
  • 3 cups milk, any kind
  • 1½ teaspoons Dijon mustard
  • ½ cup grated Parmesan cheese
  • ¼ teaspoon freshly ground black pepper

Instructions

  1. Preheat Oven and Prepare Baking Dish: Preheat the oven to 400°F. Lightly grease a 9×13-inch baking dish to prevent sticking.
  2. Blanch the Green Beans: Bring a large pot of salted water to a boil. Prepare a large bowl of ice water nearby. Drop the green beans into the boiling water and blanch for 4 minutes until just tender. Drain quickly and immerse immediately in the ice water to stop the cooking process. Drain again and dry the beans thoroughly on a towel.
  3. Cook Mushrooms: Heat olive oil in a large skillet over medium heat. Add the sliced mushrooms and cook for 8 to 10 minutes until they become soft and release their moisture.
  4. Add Flavorings: Stir in tamari, minced garlic, and fresh thyme leaves to the mushrooms and cook briefly to combine flavors.
  5. Make the Sauce: Sprinkle the flour over the mushroom mixture and stir to coat. Gradually add the milk and Dijon mustard while stirring continuously to avoid lumps. Simmer the sauce for 15 to 20 minutes, whisking often until it thickens.
  6. Finish the Sauce: Stir in the grated Parmesan cheese and freshly ground black pepper. Remove from heat.
  7. Assemble the Casserole: Spread one third of the mushroom sauce evenly in the bottom of the prepared baking dish. Layer the blanched green beans over the sauce. Pour the remaining mushroom sauce evenly over the beans.
  8. Add Onion Topping and Bake Covered: Sprinkle the French fried onions on top of the assembled casserole. Cover the dish and bake for 10 minutes.
  9. Bake Uncovered: Remove the cover and bake for an additional 10 minutes until the onions are crisp and golden. If the onions brown too quickly, cover the dish for the remainder of baking time.
  10. Serve: Garnish with extra Parmesan cheese if desired and serve hot.

Notes

  • For Crispy Baked Onions: Preheat oven to 450°F and line two large baking sheets with parchment paper. Thinly slice 2 medium yellow onions. Toss with 4 teaspoons olive oil, ½ cup all-purpose flour, 2 tablespoons panko breadcrumbs, and ½ teaspoon sea salt. Spread evenly and bake 25 to 35 minutes, tossing every 10 minutes until crispy and lightly browned.
  • Vegan Option: Omit the Parmesan cheese and add extra salt to the mushroom sauce to enhance flavor.
  • Ensure green beans are dried well after blanching to avoid sogginess in the casserole.
  • If using regular milk, whole or 2% works best for a creamy sauce; dairy alternatives like almond or oat milk can be used but may alter flavor slightly.
  • Using tamari instead of soy sauce keeps the dish gluten-free and adds rich umami.

Nutrition

  • Serving Size: 1 cup
  • Calories: 220 kcal
  • Sugar: 4 g
  • Sodium: 350 mg
  • Fat: 12 g
  • Saturated Fat: 3 g
  • Unsaturated Fat: 8 g
  • Trans Fat: 0 g
  • Carbohydrates: 20 g
  • Fiber: 4 g
  • Protein: 8 g
  • Cholesterol: 10 mg

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