Name: Creamy Mushroom Green Bean Casserole with 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)

If you’re anything like me and love that cozy, comforting vibe of a classic side dish but want to take it up a notch, you’re going to adore this Creamy Mushroom Green Bean Casserole with Crispy Onions Recipe. It’s everything you love about green bean casserole — creamy sauce, tender beans, that irresistible crunch on top — but made from scratch with fresh ingredients. Trust me, once you try this version, you’ll never look back to those canned soups and soggy onions again!

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Why You’ll Love This Recipe

Fresh Ingredients Make a Huge Difference: Using fresh green beans and mushrooms transforms this dish into something vibrant and full of flavor.
Creamy, But Not Heavy: The homemade mushroom sauce is silky and rich without being overly heavy or processed.
That Crispy Onion Topping: The crunchy baked onions are the ultimate finishing touch that gives you texture contrast and that classic green bean casserole feel.
Versatile & Crowd-Pleasing: Whether it’s holiday dinner or a weeknight side, this recipe always comes out a winner with family and friends.

A rectangular gray baking dish on a white marbled surface holds neatly arranged green beans forming the bottom layer. Above the beans, there is a thick light brown mushroom sauce with visible mushroom slices covering the center. A woman's hands are adding a top layer of thin, crispy golden onion strings, some of which are still on a small round white plate to the side. The contrast between the fresh green beans, creamy sauce, and crunchy onion topping is clear and appealing. Photo taken with an iphone --ar 4:5 --v 7

Ingredients You’ll Need

The magic of this Creamy Mushroom Green Bean Casserole with Crispy Onions Recipe lies in the way these ingredients work together — fresh, simple, and flavorful. I always suggest picking the freshest green beans you can find, and don’t skip on good quality mushrooms; cremini gives the sauce a lovely depth.

Green beans: Fresh and vibrant green beans give the casserole that crisp-tender texture you’ll love.
Extra-virgin olive oil: Adds a delicate richness and helps cook the mushrooms perfectly.
Cremini mushrooms: These bring earthiness and body to the creamy sauce.
Tamari: A great gluten-free alternative to soy sauce for depth of flavor.
Garlic cloves: Fresh garlic brightens up the mushroom sauce wonderfully.
Fresh thyme leaves: Adds an herbaceous note that pairs perfectly with mushrooms.
All-purpose flour: The thickening agent for that luscious sauce.
Milk (any kind): I like whole milk, but any milk works to keep the sauce silky.
Dijon mustard: Just a touch lifts the sauce with a subtle tang.
Parmesan cheese: Adds a nutty, savory depth — don’t be shy with it.
Freshly ground black pepper: For gentle heat and flavor balance.
French fried onions or homemade crispy baked onions: The crunchy topping that makes this casserole unforgettable.

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.

Variations

I love making this recipe my own depending on the season or what’s in my kitchen. Don’t hesitate to tweak it for your taste buds or dietary preferences — that’s half the fun of cooking homemade casseroles!

Mushroom Mix-Up: I sometimes swap cremini mushrooms for shiitake or a wild mushroom blend to deepen the flavor even more.
Dairy-Free Version: Use almond or oat milk and skip the parmesan, or substitute with nutritional yeast for a similar umami kick.
Make It Vegan: Replace butter with olive oil, use non-dairy milk, and top with crispy fried shallots instead of traditional onions.
Add Crunch Twist: Mixing panko breadcrumbs with the crispy onions gives an extra crunch that my family goes nuts for.

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

Step 1: Blanch the Green Beans to Perfection

Start by bringing a large pot of salted water to a boil. While it heats, get a bowl of ice water ready — this is key to keeping your green beans that beautiful bright green and crisp-tender. Once boiling, add your trimmed and halved green beans, blanching them for about 4 minutes. Don’t overdo it here; we want tender but with a bit of snap. Drain quickly and plunge them into the ice water bath to stop cooking instantly. Trust me, this little step makes all the difference between mushy beans and perfectly vibrant ones. After chilling, drain and pat them dry with a kitchen towel.

Step 2: Sauté Mushrooms and Build the Flavor Base

Heat two tablespoons of olive oil in a large skillet over medium heat. Add your sliced cremini mushrooms and cook, stirring occasionally, until they release their moisture and soften, about 8 to 10 minutes. This step is where your kitchen will start smelling like heaven! Once the mushrooms are soft, stir in the tamari, minced garlic, and fresh thyme leaves. Let those flavors mingle for a minute or two — the tamari adds a nice umami depth you won’t want to skip.

Step 3: Create That Silky, Creamy Mushroom Sauce

Sprinkle all-purpose flour over the mushrooms and stir well to coat everything evenly. This will thicken the sauce beautifully. Slowly whisk in the milk of your choice along with the Dijon mustard. Keep the heat on low to medium and stir frequently to avoid lumps while the sauce gently simmers. This can take 15 to 20 minutes, but patience here yields the creamiest, luscious base. Once thickened, stir in the grated Parmesan cheese and freshly ground black pepper for that final savory touch.

Step 4: Assemble and Bake Your Casserole

Preheat your oven to 400°F and lightly grease a 9×13-inch baking dish. Spread about one-third of your creamy mushroom sauce on the bottom of the dish, then layer your blanched green beans evenly on top. Pour the remaining sauce over the beans, making sure everything is nicely coated and cozy. Now for the exciting part: sprinkle a generous layer of French fried onions or your crispy baked onions over the top. Cover the dish with foil and bake for 10 minutes, then uncover and bake for another 10 minutes to let those onions crisp up perfectly. Keep an eye on the topping — if your onions start browning too much, just cover the dish lightly for the remaining bake time.

If you want, add a little extra Parmesan sprinkled on top as soon as it’s out of the oven for that extra cheesy finish. Serve it hot, and prepare for everyone to ask for seconds!

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

Don’t Skip the Ice Bath: This is key to locking in that bright green color and crunch in your green beans.
Cook Mushrooms Low and Slow: Rushing mushrooms makes them chewy; a gentle sauté brings out their natural sweetness.
Use Fresh Thyme, Not Dried: Fresh thyme adds a subtle lift you just can’t replicate with dried herbs.
Watch Your Topping: If your onions start to get too brown, cover the casserole loosely with foil to prevent burning.

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

A rectangular metal baking dish filled with three visible layers: the bottom layer is bright green whole green beans that line the dish evenly; the middle layer is scattered creamy mushroom sauce with light brown sliced mushrooms mixed in; and the top layer is a thick pile of thin, golden-brown crispy fried onion strings that cover the center of the dish more heavily with some pieces spread around the edges. The dish sits on a white marbled surface with a grey cloth partially visible on the left side. Photo taken with an iphone --ar 4:5 --v 7

Garnishes

I usually keep garnishes simple here—just a sprinkle of extra Parmesan cheese right after baking. Sometimes I add a few sprigs of fresh thyme or a light dusting of cracked black pepper. It adds a lovely fresh pop without messing with that comforting vibe.

Side Dishes

This casserole pairs beautifully with roasted turkey or chicken, mashed potatoes, and cranberry sauce if you’re doing a holiday spread. On a regular weeknight, I like it alongside grilled pork chops or even a simply roasted salmon — it’s surprisingly versatile!

Creative Ways to Present

For a special occasion, I sometimes make individual ramekin versions of this casserole — they look adorable and give everyone their own perfectly crispy topping. You could also serve it in a pretty ceramic dish if you’re hosting, making it part of a festive table centerpiece.

Make Ahead and Storage

Storing Leftovers

Leftovers? Absolutely delicious! I cool the casserole to room temp, cover tightly with foil or plastic wrap, and store it in the fridge for up to 3 days. Just keep the topping separate if you want to keep those onions crispy.

Freezing

I’ve frozen this casserole a couple of times and it reheats wonderfully. I suggest freezing it without the crispy onions on top — add those fresh after reheating for the best texture. Wrap tight with foil or use an airtight container and freeze for up to 2 months.

Reheating

To reheat, I pop the casserole uncovered in a 350°F oven for about 20 minutes (longer if frozen), then add fresh crispy onions on top and bake a final 5-7 minutes until crunchy and golden. This keeps everything tasting fresh and crisp!

FAQs

Can I make the Creamy Mushroom Green Bean Casserole with Crispy Onions Recipe ahead of time?

Yes! You can assemble the casserole a day ahead and refrigerate it covered; just add the crispy onions on top right before baking to keep them crunchy. It’s a fantastic make-ahead dish for busy holiday cooking.
What’s the best way to get crispy onions without store-bought ones?

I love making my own crispy baked onions by thinly slicing onions, coating them lightly with oil and seasoning, then baking them on a wire rack until golden and crunchy. They’re fresher and less oily than store-bought, and my family swears by them.
Can I use frozen green beans in this recipe?

You can, but I highly recommend fresh if possible. Frozen beans tend to get softer and less vibrant after blanching and baking. If using frozen, thaw completely and drain well to avoid excess moisture.
Is this recipe gluten-free?

Not as is because of the all-purpose flour and typical French fried onions. However, you can substitute a gluten-free flour blend and find gluten-free crispy onion toppings to make it safe for gluten-sensitive diets.

Final Thoughts

This Creamy Mushroom Green Bean Casserole with Crispy Onions Recipe holds a special place in my heart because it turns a humble side dish into something extraordinary — rich, fresh, and crunchy all in one bite. I love sharing this with friends and family, especially during holidays when everyone’s craving comfort food but something a bit more homemade and thoughtful. Give it a try, and I’m sure it’ll become a beloved staple on your table just like it did in mine!