Ingredients: 1 ½ pounds fresh green beans, trimmed and cut into 2-inch pieces 1 medium onion, finely chopped 2 cloves garlic, minced 8 oz mushrooms, sliced (optional) 3 tablespoons butter 3 tablespoons all-purpose flour 1 ½ cups milk (whole or 2%) 1 cup chicken or vegetable broth 1 cup shredded cheddar cheese ½ cup grated Parmesan cheese 1 cup crispy fried onions (store-bought or homemade) Salt and pepper to taste
1. Preheat the oven to 350 degrees F (175 degrees C). Fill a large bowl with ice and cold water.
2. Bring a large pot of lightly salted water to a boil. Add green beans and cook, uncovered, until crisp-tender, about 6 minutes. Drain in a colander and immediately immerse in ice water for several minutes to stop the cooking process. Drain and transfer to a large bowl.
3. Heat 3 tablespoons butter in a large skillet over medium-high heat. Add onions; sauté until translucent, about 5 minutes. Add mushrooms and garlic; sauté until mushrooms just cooked through, about 5 minutes. Stir into green beans.
4. Place remaining 5 tablespoons butter in a 2-quart, microwave-safe bowl. Microwave on high power in 30 second intervals, until melted.
5. Whisk flour into melted butter until smooth; season with sea salt and black pepper. Add 1 cup milk; whisk until smooth and combined. Microwave for 2 minutes. Add 1 cup milk, whisking until smooth; microwave for 2 minutes. The roux mixture should thicken between additions, less so as each cup milk is added. Add remaining 1 cup of milk; microwave for 2 minutes more, then whisk until smooth. 3.
6. Transfer green bean mixture to a 9x13-inch baking pan; stir in thickened roux to combine. Season with salt and black pepper.
7. Bake in the preheated oven until warm and bubbly, about 30 minutes. Top with crispy fried onions and return to the oven for 5 minutes.