Bring salted water to a boil in medium saucepan. Break the macaroni tubes into thirds and add to the boling water. Cook uncovered until macaroni is tender but still firm. Preheat oven to 350F (180C). Drain the macaroni and return to the saucepan. Add the onion, cheese, milk, ketchup, mustard and egg. Add salt and pepper to taste. Herbs such as marjoram and thyme can also be added. Pour into a greased dish and top with more grated cheese. Fine breadcrumbs can also be added as a topping. Bake for 30-40 minutes or until golden brown. Macaroni pie can be served as a side with fish, chicken, pork, stew... whatever you wish really.