Description

This Best-Ever Green Bean Casserole combines fresh green beans with sautéed crimini mushrooms in a creamy, garlicky béchamel sauce topped with crispy French’s fried onions. Baked to bubbling perfection and browned on top, this classic comfort dish offers a flavorful twist with fresh ingredients and rich Parmesan cheese.

Ingredients

Scale

Vegetables

2 lb. fresh green beans
1 lb. crimini mushrooms, sliced (divided into ½ lb. portions)
4 large sprigs thyme (divided into 2 sprigs each)
4 garlic cloves, finely grated

Fats & Oils

2 Tbsp. extra-virgin olive oil, divided
6 Tbsp. unsalted butter, divided

Dairy

1¼ cups whole milk
1 cup heavy cream
½ cup grated Parmesan cheese

Pantry

Kosher salt
2 Tbsp. all-purpose flour
Freshly ground black pepper
¾ cup French’s fried onions

Instructions

Blanch the Green Beans: Place a rack in the middle of the oven and preheat to 375°F. Bring a large pot of salted water to a boil. Working in batches, cook the fresh green beans until bright green and half tender, about 3 minutes per batch. Drain and allow to cool, then trim the stem ends.
Sauté Half the Mushrooms: Heat 1 tablespoon of extra-virgin olive oil in a large skillet over medium-high heat. Add half the sliced crimini mushrooms and cook without stirring for 2 minutes to brown the underside. Toss and continue cooking, tossing occasionally, until the mushrooms are browned on both sides, about 3 more minutes. Add 2 tablespoons unsalted butter and 2 sprigs of thyme, tossing occasionally until the butter browns and mushrooms are very tender, about 4 minutes. Season with kosher salt and transfer to a plate.
Sauté Remaining Mushrooms: Repeat the process with the remaining 2 tablespoons unsalted butter, 1 tablespoon olive oil, the rest of the mushrooms, and thyme sprigs. Season with salt and set aside.
Make Béchamel Sauce: Melt the remaining 2 tablespoons butter in a large saucepan over medium-low heat. Whisk in 2 tablespoons all-purpose flour and cook until the roux is golden brown and fragrant, about 4 minutes. Gradually whisk in the whole milk and heavy cream, increase the heat, and bring to a simmer while whisking often. Cook until the sauce thickens and bubbles, about 5 minutes. Remove from heat, then whisk in the grated garlic and Parmesan cheese. Season with kosher salt and freshly ground black pepper to taste.
Assemble and Bake: Arrange the blanched green beans and sautéed mushrooms evenly in a 2-quart baking dish. Pour the béchamel sauce over the vegetables—it may seem a bit thin but will thicken during baking. Cover tightly with foil and bake for 25–30 minutes until the sauce is bubbling.
Bake Until Golden: Remove the foil and continue baking uncovered for 15–20 minutes until the casserole is lightly browned on top and around the edges.
Add Fried Onions and Finish Baking: Sprinkle ¾ cup French’s fried onions evenly over the top. Bake for an additional 3 minutes until the onions are slightly darker and fragrant.
Set Before Serving: Let the casserole sit for 10 minutes to set before serving to allow the sauce to thicken fully and flavors to meld.

Notes

Blanching the green beans ensures they stay bright and retain a slight crunch after baking.
Sauté mushrooms in batches to achieve a deeply browned, caramelized flavor.
The béchamel sauce provides a rich and creamy base, enhanced with garlic and Parmesan for extra depth.
Covering the casserole during initial baking helps the sauce cook without drying out.
Allowing the dish to rest after baking improves texture and flavor melding.
French’s fried onions add a crunchy, savory topping that contrasts beautifully with the creamy interior.

Prep Time: 20 minutes
Cook Time: 1 hour
Category: Casserole
Method: Baking
Cuisine: American

Keywords: green bean casserole, mushroom casserole, holiday side dish, baked casserole, creamy green beans