3 cups (12 ounces) elbow macaroni
3 tablespoons butter
1/4 cup white onion, finely diced
3 tablespoons flour
2 cups warm milk
1/2 teaspoon ground white pepper
1 tablespoon prepared mustard
1 1/2 cups (6 ounces) Fontina Cheese, shredded
1 1/2 cups (6 ounces) Provolone Cheese, shredded
2 ounces prosciutto, diced
1 tablespoon minced fresh flat leaf parsley
Preheat oven to 375° F.
Cook macaroni according to the package instructions, or until al dente. Drain, rinse, and set aside.
Melt butter in large saucepan, add onion and sauté for 2 minutes or until transparent. Blend in flour, stirring well to incorporate, and cook for an additional minute. Whisk the milk into butter-and-flour mixture. Bring to simmer and cook, stirring constantly, until sauce thickens.
Reduce to low heat and add pepper and mustard. Mix the Fontina and Provolone Cheeses. Stir 2 1/2 cups of the cheeses into the sauce. Add cooked macaroni and prosciutto to cheese sauce, and mix well. Place macaroni mixture in buttered, oven-proof, 9 x 9-inch dish. Sprinkle with remaining 1/2 cups of cheese.
Bake for 30 minutes or until top is golden brown. Sprinkle the surface with parsley just before serving.