# What You'll Need:
→ Vegetables
01 - 2 pounds fresh green beans, trimmed and cut into 2-inch pieces (or 2 pounds frozen cut green beans, thawed and drained)
→ Sauce Base
02 - 2 tablespoons unsalted butter
03 - 9 ounces cremini or button mushrooms, sliced
04 - 1 small yellow onion, finely chopped
05 - 2 garlic cloves, minced
06 - 2 tablespoons all-purpose flour
07 - 1 cup whole milk
08 - ½ cup heavy cream
09 - ½ cup low-sodium vegetable broth
10 - 1 teaspoon salt
11 - ½ teaspoon ground black pepper
12 - ½ teaspoon ground nutmeg (optional)
→ Topping
13 - 1½ cups crispy fried onions (store-bought or homemade)
# Method Steps:
01 - Set the oven temperature to 350°F.
02 - Bring a large pot of salted water to a boil, add green beans, and cook for 5 minutes until tender-crisp and vibrant green; drain and rinse immediately under cold water to halt cooking.
03 - In a large skillet over medium heat, melt butter. Add mushrooms and cook for 5-6 minutes until browned. Incorporate onion and garlic, sautéing another 2-3 minutes until softened.
04 - Sprinkle in flour and stir constantly for 1 minute. Gradually whisk in milk, cream, and vegetable broth. Simmer until sauce thickens, approximately 5 minutes. Season with salt, pepper, and optional nutmeg.
05 - Add drained green beans to the skillet and fold them into the sauce until evenly coated.
06 - Transfer the mixture into a 2-quart baking dish. Evenly sprinkle half of the crispy fried onions over the top.
07 - Place the dish in the oven and bake for 25 minutes until bubbling.
08 - Remove from oven, evenly distribute the remaining fried onions, and bake for an additional 5 to 7 minutes until the topping is golden and crisp.
09 - Allow the casserole to cool for 5 minutes before serving.
