6 ounces (2 cups) elbow macaroni
4 tablespoons unsalted butter, divided
2 tablespoons all-purpose flour
1 1/4 cups whole milk
8 ounces (2 cups) cheddar cheese, shredded
1/4 teaspoon dry mustard
1/4 teaspoon salt
1/4 teaspoon fresh ground pepper
1 egg, lightly beaten
1/2 cup Italian style breadcrumbs