# What You'll Need:
→ Vegetables
01 - 2 lb fresh green beans, trimmed and cut into 2-inch pieces (or 2 lb frozen cut green beans, thawed and drained)
→ Sauce Base
02 - 2 tbsp unsalted butter
03 - 9 oz cremini or button mushrooms, sliced
04 - 1 small yellow onion, finely chopped
05 - 2 garlic cloves, minced
06 - 2 tbsp all-purpose flour
07 - 1 cup whole milk
08 - ½ cup heavy cream
09 - ½ cup low-sodium vegetable broth
10 - 1 tsp salt
11 - ½ tsp black pepper
12 - ½ tsp ground nutmeg (optional)
→ Topping
13 - 1½ cups crispy fried onions (store-bought or homemade)
# Cooking Steps:
01 - Set oven temperature to 350°F.
02 - Bring a large pot of salted water to a boil. Cook green beans for 5 minutes until tender-crisp and bright green. Drain and rinse under cold water to halt cooking. Set aside.
03 - In a large skillet over medium heat, melt butter. Sauté mushrooms for 5 to 6 minutes until browned and tender. Add onion and garlic; cook 2 to 3 minutes until softened.
04 - Sprinkle flour over the mixture and cook, stirring constantly, for 1 minute. Gradually whisk in milk, heavy cream, and vegetable broth. Simmer until sauce thickens, about 5 minutes. Season with salt, pepper, and optional nutmeg.
05 - Add drained green beans to the skillet and toss carefully to coat them evenly with the sauce.
06 - Transfer mixture into a 2-quart baking dish. Evenly sprinkle half of the crispy fried onions on the surface.
07 - Bake for 25 minutes until the casserole bubbles.
08 - Remove from oven, evenly scatter remaining fried onions over the top, and return to oven for 5 to 7 minutes until golden brown and crisp.
09 - Allow casserole to cool for 5 minutes before serving.
