Gruyère Prosciutto Mac and Cheese

First time I'm making this recipe.  I added Monterey Jack cheese to this recipe and sprinkled gruyere cheese on top.

Kosher salt
Vegetable oil
1 pound elbow macaroni
1 quart milk
8 tablespoons (1 stick) unsalted butter, divided
1/2 cup all-purpose flour
12 ounces Gruyère cheese, grated (4 cups)
8 ounces extra-sharp Cheddar, grated (2 cups)
6 oz Prosciutto
1/2 teaspoon freshly ground black pepper
1/2 teaspoon nutmeg

Preheat the oven to 375 degrees.

Drizzle oil into a large pot of boiling salted water. Add the macaroni and cook according to the directions on the package, 6 to 8 minutes. Drain well.

Meanwhile, heat the milk in a small saucepan, but don’t boil it. Melt 6 tablespoons of butter in a large (4-quart) pot and add the flour. Cook over low heat for 2 minutes, stirring with a whisk. While whisking, add the hot milk and cook for a minute or two more, until thickened and smooth. Off the heat, add the Gruyère, Cheddar, 1 tablespoon salt, pepper, prosciutto, and nutmeg. Add the cooked macaroni and stir well. Pour into a 3-quart baking dish.

Bake for 30 to 35 minutes, or until the sauce is bubbly and the macaroni is browned on the top.