best cheesy macaroni recipe

Ingredients: 1 pound elbow macaroni (or your favorite pasta shape) 4 tablespoons unsalted butter 1/4 cup all-purpose flour 3 cups whole milk 1 cup heavy cream 4 cups shredded sharp cheddar cheese 1 cup shredded mozzarella cheese 1 teaspoon Dijon mustard (optional) Salt and black pepper to taste