Name: Green Bean Casserole with Cremini Mushrooms and Crispy Onions Recipe
Prep time: 20 min
Cook time: 1 h
Total time: 1 h 20 min
Cuisine: American
Ingredients: 1½ pounds green beans, trimmed and halved; 16 ounces cremini mushrooms, sliced; 4 garlic cloves, minced; 2 tablespoons fresh thyme leaves; 2 tablespoons extra-virgin olive oil; 2 tablespoons tamari; ¼ cup all-purpose flour; 3 cups milk, any kind; 1½ teaspoons Dijon mustard; ½ cup grated Parmesan cheese, plus more for sprinkling; ¼ teaspoon freshly ground black pepper; 1½ cups French fried onions, or homemade Crispy Baked Onions (see recipe notes)

Jump to Recipe·5 from 18 reviews

If you’re a fan of classic comfort food but want to take green bean casserole to the next level, you are going to LOVE this Green Bean Casserole with Cremini Mushrooms and Crispy Onions Recipe. It’s my go-to whenever I want something warm, savory, and downright satisfying, but with a fresh twist thanks to cremini mushrooms and those irresistible crispy onions. Trust me, once you try it, you’ll never go back to the canned soup version!

❤️

Why This Recipe Works

Fresh Ingredients: Using fresh green beans and cremini mushrooms delivers better texture and a deep, earthy flavor that canned soup versions can’t match.
Homemade Sauce: The mushroom sauce thickened with flour and infused with garlic, thyme, and Parmesan creates a creamy, rich base that’s full of flavor and comforting indulgence.
Crispy Onions: Topping the casserole with French fried onions or my homemade crispy baked onions adds an irresistible crunch and golden finish that everyone will rave about.
Balanced Layers: Blanching the green beans keeps them tender yet crisp, while layering them with sauce ensures every bite is perfectly coated and satisfying.

Green Bean Casserole with Cremini Mushrooms and Crispy Onions, healthy green bean casserole, homemade green bean casserole, mushroom green bean bake, festive vegetable side dish - 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

Ingredients & Why They Work

Every ingredient in this Green Bean Casserole with Cremini Mushrooms and Crispy Onions Recipe plays an important role, balancing texture and flavor for a casserole that’s moist but not soggy, creamy but not heavy. Here’s what you need and why I love each component.

Green beans: Fresh and trimmed, these bring that classic snap and vibrant color that frozen or canned just can’t replicate.
Extra-virgin olive oil: The perfect fat to sauté mushrooms with a subtle richness that builds layers of flavor.
Cremini mushrooms: Their earthy flavor deepens the sauce and adds meaty texture without overwhelming the dish.
Tamari: Adds umami and a slight saltiness that complements the mushrooms and balances the creamy sauce.
Garlic: Freshly minced to awaken the entire dish with aromatic depth.
Fresh thyme leaves: This herb brightens and lifts the earthy, creamy sauce, making it wonderfully fragrant.
All-purpose flour: Used to thicken the sauce just right, creating a luscious coating for the beans.
Milk (any kind): The creamy base for the sauce; I like whole milk for richness, but any works.
Dijon mustard: Adds a subtle tang that wakes up the sauce – don’t skip it even though it’s a small amount.
Parmesan cheese: For that salty, nutty boost that makes this casserole feel special and more savory.
Black pepper: Freshly ground for a touch of heat and depth.
French fried onions or homemade crispy onions: The crown jewel for crunch and golden goodness on top.

📝

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 personalizing this casserole depending on who I’m cooking for and what I have on hand. Feel free to make it your own by playing with different mushrooms, spices, or toppings. It’s a flexible recipe that welcomes you to get creative!

Variation: I once swapped cremini mushrooms for shiitake to give it a more intense umami kick — it was delicious and a big hit at dinner.
Dietary preference: For a vegan twist, leave out the Parmesan and use non-dairy milk; add a pinch extra salt to balance flavor.
Extra herbs: Try fresh rosemary or sage if you want a more autumnal vibe — it pairs beautifully with green beans and mushrooms.
Crispy topping alternative: Homemade panko breadcrumbs toasted with a little olive oil work great if you want to skip the fried onions.

Step-by-Step: How I Make Green Bean Casserole with Cremini Mushrooms and Crispy Onions Recipe

Step 1: Prep and Blanch Your Green Beans

Start by trimming and halving your fresh green beans. Then bring a large pot of salted water to a boil—you want it salty like the sea, trust me. Drop the beans in for precisely 4 minutes to blanch them. This step is essential: it keeps them beautifully crisp when baked, rather than mushy. Immediately transfer the beans to a big bowl of iced water to stop the cooking and retain that vivid green color. Drain again and pat dry on a towel; moisture here can make your casserole soggy later.

Step 2: Cook Your Mushrooms and Build the Sauce

Heat olive oil in a large skillet over medium heat and sauté sliced cremini mushrooms until they’re soft and release their lovely juices—about 8 to 10 minutes. Then add tamari, minced garlic, and fresh thyme leaves for flavor layering; cook for a minute to let those aromas bloom. Sprinkle flour evenly over the mushrooms and stir well to coat — this helps thicken the sauce. Slowly pour in milk while whisking to avoid lumps, and stir in Dijon mustard. Let it simmer gently for 15 to 20 minutes, whisking often, until the sauce thickens up beautifully. Finish by stirring in Parmesan cheese and freshly ground black pepper for that savory punch.

Step 3: Assemble and Bake Your Casserole

Spoon about one-third of your mushroom sauce into the bottom of a greased 9×13-inch baking dish. Spread the blanched green beans evenly on top, then pour the remaining sauce over the beans to coat every bit. Sprinkle the French fried onions or your homemade crispy onions generously over the top—this is what’ll give you that irresistible crunch. Cover the casserole with foil and bake in a preheated 400°F oven for 10 minutes. Then remove the foil and bake for an additional 10 minutes until the onions are golden and crispy. If you notice the onions browning too fast, pop the foil back on to keep them from burning. I sometimes sprinkle a bit more Parmesan cheese before serving for an extra gooey finish.

💡

Pro Tips for Making Green Bean Casserole with Cremini Mushrooms and Crispy Onions Recipe

Don’t Skip Blanching: It locks in color and texture, so your beans don’t turn mushy once baked.
Simmer the Sauce Slowly: To avoid lumps and get that velvety texture, whisk constantly once you add milk.
Fresh Thyme Over Dried: I’ve found fresh herbs add a wonderful brightness that dried just can’t match in this dish.
Manage Onion Browning: Keep foil handy during baking to cover onions if they brown too fast and prevent burning.

How to Serve Green Bean Casserole with Cremini Mushrooms and Crispy Onions Recipe

Garnishes

I usually keep it simple with a sprinkle of extra grated Parmesan right before serving. If I’m feeling fancy, a few fresh thyme sprigs or chopped parsley add a pop of color and freshness to contrast the rich sauce and crispy onions.

Side Dishes

This casserole pairs beautifully with roast chicken, turkey, or even a vegetarian main like stuffed portobellos. I often serve it alongside mashed potatoes or a crisp green salad to balance the richness.

Creative Ways to Present

For holiday dinners, I like to serve individual portions in ramekins topped with little thyme sprigs—makes it feel extra special. Or you can create a green bean “tower” by layering in a clear trifle dish to show off all the creamy, crunchy layers.

Make Ahead and Storage

Storing Leftovers

Leftover casserole keeps really well in an airtight container in the fridge for 3 to 4 days. I find the crispy onions soften a bit overnight, so I usually sprinkle on fresh ones before reheating for that extra crunch.

Freezing

I’ve frozen this casserole a few times with good results. Freeze before baking, wrapped tightly, and thaw overnight in the fridge before cooking as directed. Just add the crispy onions fresh at bake time to keep them crunchy.

Reheating

To reheat, I cover the casserole loosely with foil and bake in a 350°F oven until warmed through, about 20 minutes. If you want to crisp the topping again, remove the foil for the last 5 minutes.

FAQs

Can I use frozen green beans instead of fresh in this recipe?

Yes, but I recommend thawing and drying them thoroughly before using. Because frozen green beans are already softened, you may want to reduce blanching time or skip it to avoid them becoming mushy after baking.
How do I make homemade crispy onions for the topping?

Thinly slice yellow onions, toss with olive oil, flour, panko bread crumbs, and salt, then bake on parchment-lined sheets at 450°F, tossing every 10 minutes until golden and crisp, about 25-35 minutes. They’re a crunchy, healthier alternative to store-bought fried onions!
Is this recipe suitable for vegans?

Absolutely! Simply omit the Parmesan cheese and use plant-based milk. Adding a little extra salt helps balance flavors without the cheese.
Can I prepare this casserole in advance?

Yes, you can assemble it a day ahead, cover, and keep it refrigerated. Add the crispy onions and bake just before serving to keep the topping extra crunchy.

Final Thoughts

I’ll be honest: This Green Bean Casserole with Cremini Mushrooms and Crispy Onions Recipe feels like a hug on a plate. It’s cozy, flavorful, and has just the right amount of crunch. Over the years, it’s become a staple for holidays and family dinners because it’s so reliable and absolutely delicious. I’m excited for you to give it a try and maybe even make it your own — you’ll have your friends and family asking for seconds, I promise.