Put 1 litre of milk into a bowl and soak the herring in it overnight.. remove the and pat dry being sure to remove any and all bones. Coaresly chop the herring. Fry the onions in 2 T of butter until golden. Pan fry the ground meats seperately and place into a food processor/blander. Add the onion, herring, & potatos. Chop/blend untilt soooth mixture is formed. Stir in ther sour cream and egg yolks then add the spices. Beat the egg whites until they are stiff but not dry. Preheat the oven to 200ºC . & grease a 2 litre baking dish. Stir in the egg whites and mix until Fold in the egg whites at this point and turn the mixture into the greased baking dish. Sprinkle with the bread crumbs and parmesan cheese, dot with the remaining butter, & then bake for 40 minutes. Serve hot.