Recipe: Loaded Baked Potato Casserole

Name: Recipe: Loaded Baked Potato Casserole
Ingredients: 6 tablespoons unsalted butter, divided; 6 large russet potatoes, baked (2 to 2 1/4 pounds); 1 1/2 teaspoons kosher salt, divided; 1/2 teaspoon freshly ground white pepper, divided; 3 tablespoons all-purpose flour; 1 cup whole or 2% milk; 1 cup sour cream; 1/2 cup shredded Parmesan cheese; 2 1/2 cups shredded extra-sharp Cheddar cheese, divided; Cooking spray; 1 pound frozen broccoli, thawed and drained; 1 large bunch fresh chives, cut into 1/4-inch pieces, divided; 10 to 12 slices smoked bacon, cooked and cut or broken into 1/4-inch pieces; 1 to 2 teaspoons red pepper flakes