Broccoli and Cheese Casserole with Crunchy Topping | America's Test Kitchen

Ingredients

• 3/4 cup panko bread crumbs
• 1 ounce Parmesan cheese , grated (1/2 cup)
• 3 tablespoons unsalted butter , melted, plus 3 tablespoons unsalted butter
• Salt and pepper
• 2 pounds broccoli florets , cut into 1-inch pieces
• 1 shallot , minced
• 2 garlic cloves , minced
• 3 tablespoons all-purpose flour
• 3 cups half-and-half
• 6 ounces extra-sharp cheddar cheese , shredded (1½ cups)
• 2 ounces American cheese , chopped (1/2 cup)
• 2 teaspoons hot sauce
• 1 teaspoon dry mustard