Clean a pike and slit it along the backbone. Carefully remove the skin without piercing it. Set aside the head and tail, then separate the flesh from the bones. Salt the flesh and finely chop with 1 onion and several cleaned Black Sea sprats. Add a roll that has been soaked in milk and squeezed out and mix in 1 spoon butter. Add a little nutmeg, pepper, salt, and 1–2 eggs. Pound the mixture in a mortar, stuff the pike skin, and sew it up. Grease a roasting pan with butter. Lay the pike on wooden spills and tie up with string. Transfer the fish tied in its spills to the roasting pan, pour on butter and sour cream, and set in the oven. Baste the fish several times with this sauce while it is cooking. When the pike has browned on both sides, carefully transfer it to a platter and remove the string and the wooden spills. Pour the pan juices over the fish.