Green Bean and Wisconsin Gruyere Casserole with Spicy Onion Rings - Brennans Market

Ingredients

• 5 Tablespoons butter, divided
• 1/2 pound sliced mushrooms
• salt and pepper to taste
• 1/2 cup flour, divided
• 2 1/4 cups (2 percent reduced fat) milk, divided
• 2 cups Wisconsin Gruyere Cheese, shredded, divided
• 2 pounds fresh green beans, trimmed, left whole and steamed or precooked for 5 minutes
• 1 yellow onion, sliced into thin rings
• 1/4 cup fine dried bread crumbs
• 1/8 to 1/4 teaspoon cayenne pepper