Cheesy Mashed Potato Casserole with Blue Cheese, Bacon and Rosemary | America's Test Kitchen

Ingredients

• 4 pounds Yukon Gold potato , peeled and sliced ½ inch thick
• 1 teaspoon table salt , plus salt for cooking potatoes
• 16 tablespoons unsalted butter , cut into 16 pieces
• 1 1/2 cups half-and-half
• 1 teaspoon pepper
• 6 ounces whole-milk mozzarella cheese , shredded (1½ cups)
• 4 ounces blue cheese , crumbled (1 cup)
• 12 ounces cooked bacon , crumbled (1 cup)
• 2 teaspoons minced fresh rosemary
• 3/4 cup panko bread crumbs
• 2 tablespoons unsalted butter , melted