1Preheat oven to 350°F. Prepare pasta according to package directions for al dente.
2Melt butter in a large saucepan over medium heat. Add grated onion, dry mustard, salt, pepper, nutmeg, and cayenne pepper; cook, stirring, 30 seconds.
3Add flour and cook, stirring, until golden, about 2 minutes.
4Gradually whisk in milk and cream. Bring to a boil, whisking occasionally.
5Reduce heat to medium-low; simmer, whisking, until slightly thickened, about 5 minutes.
6Stir in Worcestershire sauce.
7Remove from heat; stir in ¾ cup each of shredded Cheddar cheeses until melted.
8Stir in pasta and diced cheeses; pour into a lightly greased 13- x 9-inch baking dish.
9Bake on a rimmed baking sheet in the preheated oven until bubbly and golden, about 30 minutes.
10Remove from oven; increase oven temperature to broil.
11Sprinkle with reserved shredded cheeses; broil 6 inches from heat until cheeses are melted and golden, about 2 minutes.
12Remove from oven; cool slightly on a wire rack, about 15 minutes.
Ingredients
16 ounces large elbow macaroni, large shells, or cavatappi pasta