Soak the bread crumbs in the half and half for 5 minutes in a large mixing bowl.
Melt 1 tablespoon of the butter in a small skillet over low to moderate heat. When the foam starts to subside, add the onions and saute them for about 2 minutes. Let cool slightly.
Add the beef, veal, pork, egg nutmeg, salt, pepper, and onions to the bread-crumb mixture. Gently combine the ingredients with your hands.
Cover the bowl and refrigerate the mixture for a couple of hours.
Shape the meat mixture with your hands into uniform 2/3-inch balls. Arrange them on a plate in one layer so they do not touch each other. Let the meatballs stand at room temperature for 30 minutes.
Melt the remaining butter in a saute pan or skillet over moderate heat. When the foam starts to subside, add the meatballs. (Do not crowd the pan; unless your pan is oversized, you will have to cook gthe meatballs in batches and keep the cooked ones warm in a preheated 200 degree F oven.) Saute the meatballs for about 5 minutes until they become brown on all sides. Turn them as necessary, but do so gently.
Transfer the ''koettbullar'' to a warm platter and serve immediately.