Cheesy Broccoli Casserole

INGREDIENTS

3 pounds broccoli florets, cut into bite-size pieces
8 tablespoons unsalted butter, divided
1 medium yellow onion, finely chopped
8 ounces white button mushrooms, finely chopped
5 tablespoons all-purpose flour
4 cups whole milk
8 ounces sharp cheddar cheese, shredded and divided
1 teaspoon salt
1 teaspoon freshly ground black pepper
FOR THE TOPPING
30 crackers, crushed
2 tablespoons unsalted butter, melted

DIRECTIONS

1. Heat oven to 400 degrees F. Lightly grease 9x13-inch baking dish; set aside.
2. Bring large pot of water to boil. Add broccoli and boil 3 to 5 minutes. Drain and rinse with cold water.
3. In medium skillet over medium-high heat, melt 3 tablespoons butter. Add onion and mushrooms. Cook 10 minutes, stirring occasionally. Transfer to bowl and set aside.
4. In medium saucepan over medium heat, melt the remaining 5 tablespoons butter. Add flour and stir 1 to 2 minutes. Slowly begin to add milk, whisking constantly until all milk has been added. Cook 2 to 3 minutes, or until mixture begins to thicken. Add one-third shredded cheese and stir until completely melted. Remove from heat and stir in reserved onions and mushrooms. Stir in the salt and pepper.
5. Place broccoli mixture in prepared baking dish. Sprinkle with another one-third cheese. Pour sauce over broccoli. Stir with the remaining third of cheese. In small bowl, combine the cracker crumbs and melted butter until moistened. Sprinkle evenly over casserole.
6. Bake 15-20 minutes, or until top is golden brown. Remove from oven and let stand 10 minutes before serving.