Preheat oven to 400°F. Cook the rigatoni in 5 to 6 quarts salted boiling water until extra al dante (they will finish cooking in the oven). Drain well and place in a large bowl. Add 2/3 of the butter, 1/2 of the parmigiano, and nutmeg and mix well until all the pasta is coated. In a buttered baking dish, make a layer of the pasta, a layer of the fontina cheese, sprinkle with the parmigiano, and repeat the process until the pasta is used up, ending with a layer of the fontina on top. Sprinkle with parmigiano and black pepper and dot with remaining butter. Bake for 15 minutes, or until the cheese is melted. May be served on flat plates.