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 1/4 to /2-inch pieces
• 5 1/2 cups milk
• 1/2 cup all-purpose flour
• 2 t. salt, plus more for water
• 1/4 t. freshly grated nutmeg
• 1/4 t. freshly ground black pepper
• 1/4 t. cayenne pepper
• 4 1/2 cups (about 18 oz) grated sharp white cheddar cheese
• 2 cups (about 8 ounces) grated Gruyere or 1 1/4 cups (about 5 oz.) grated Pecorino Romano cheese
• 1 lb. elbow macaroni