Martha Stewart's Macaroni & Cheese

Ingredients

• 8 T. (1 stick) unsalted butter, plus more for casserole
• 6 slices good white bread, crusts removed, torn into ¼ to ½-inch pieces
• 5½ cups milk
• ½ cup all-purpose flour
• 2 t. salt, plus more for water
• ¼ t. freshly grated nutmeg
• ¼ t. freshly ground black pepper
• ¼ t. cayenne pepper
• 4 ½ cups (about 18 oz.) grated sharp white cheddar cheese
• 2 cups (about 8 oz.) grated Gruyere or 1¼ cups (about 5 oz.) grated Pecorino Romano cheese
• 1 lb. elbow macaroni