Pimiento Mac and Cheese

Name: Pimiento Mac and Cheese
Ingredients: Unsalted butter, softened, for baking dish; 1 red bell pepper; 8 ounces elbow macaroni (2 cups); Kosher salt; 11 ounces extra-sharp cheddar, 5 ounces cut into ½-inch cubes (1 ½ cups), 6 ounces coarsely grated (1 ¾ cups); 2 tablespoons plus 1 teaspoon unbleached all-purpose flour; 1 ½ teaspoons ground mustard; ⅛ teaspoon cayenne pepper; ⅛ teaspoon freshly grated nutmeg; ⅔ cup sour cream; 2 large eggs; ⅓ cup grated onion (from 1); 1 cup half and half; 1 cup heavy cream; 1 teaspoon Worcestershire sauce