Cook the pasta according to package directions, less 3 minutes of al dente. The pasta is going to continue to cook in the oven, so you don’t want to overcook it. Drain and set aside.
Cut 5 tablespoons of butter into tablespoon portions. Cut remaining 3 tablespoons of butter into 1/2 inch cubes.
Warm the cream and buttermilk in a small pan, then cover and set aside to keep warm.
Stir the pasta with the 5 tablespoons of butter in a large bowl. Pour in the warm cream and buttermilk, and fold in the Fontina until it starts to melt. Add the grated nutmeg, and season to taste with salt and pepper.
Spread the pasta mixture into the buttered baking dish. Top with breadcrumbs and grated cheese. Top with 3 tablespoons of cubed butter over the top. Bake 20-22 minutes, or until the top is slightly browned. Sprinkle fresh parsley over the top, and serve hot.