Preheat the oven to 375 degrees F.
Boil water in a large pot. Add the macaroni and cook according to the directions on the package. Drain well.
Meanwhile, heat the milk in a saucepan, but don't boil. Melt 6 tablespoons of butter in a large pot and add the flour. Cook over low heat for 2 minutes, whisking. While whisking, add the milk, pepper, nutmeg, and salt and cook for a minute or two, until thickened and smooth. Take off the heat, add the cheeses, onion, and turkey ham. Add the cooked macaroni and pour into a baking dish.
Melt the last 2 tbsps of butter and mix with bread crumbs. Sprinkle this on top.
Bake for 30 to 35 minutes, or til the sauce is bubbly.