Have the butcher grind the meat a couple of times. Soak the bread in water. While it is soaking, mince and saute the onion and mash the potatoes. Now mix all the ingredients in a large bowl; keep working the mixture until you have a smooth, spongy mass. It is best to work the mixture by hand. Heat butter (or fat) in a frying pan. Shape the balls by using a spoon and the palm of your hand, both wet. Brown evenly in the butter, shaking the pan meanwhile to keep the round shape. Remove to a kettle. Repeat until the meat mixture is used up. Make the gravy.
Make the gravy in the same frying pan. Heat the butter (or fat) and add the flour, stirring to a golden paste. Add the stock gradually, stirring briskly to avoid lumps. If you prefer a darker gravy, add a few drops of Kitchen Bouquet or brown some sugar for the purpose. Add the cream and season to taste. Simmer the sauce 4-5 minutes. Pour the gravy over the meat balls and let them and cook in it over low heat for 40-60 minutes. Neither overcooking not reheating will harm this wondeerful concoction.