Boil pasta according to package directions, undercooking slightly, and drain. Melt butter, stir in flour, and cook roux one minute. Gradually whisk in stock. Bring mixture to a boil and boil one to two minutes. Whisk in sherry and cream and bring just to a boil. Remove from heat and stir in fontina, Gruyere, and Emmenthaler cheese until the cheese melts. Season with thyme, nutmeg, salt, and pepper to taste. Pour into a 23 cm x 33 cm baking pan. Sprinkle with bread crumbs and Parmesan cheese. Bake at 190ºC or 30 minutes.