Walnut Crusted Brie Mac and Cheese

Name: Walnut Crusted Brie Mac and Cheese
Ingredients: Nonstick cooking spray, for the baking dish; 3 ounces pancetta, chopped; 8 ounces rigatoni; 3 tablespoons unsalted butter; 1/2 small onion, finely chopped; Kosher saltand freshly ground black pepper; 1/4 teaspoon ground nutmeg; 1/4 teaspoon sweet paprika; 1/4 teaspoon cayenne pepper; 1/8 teaspoon ground allspice; 1/4 cup all-purpose flour; 3 cups whole milk; 4 ounces Brie, rind removed and finely chopped; 4 ounces Gruyere, shredded; 1/2 cup walnuts, toasted and coarsely chopped; 3 tablespoons shredded Parmesan