Soak 2 good Scottish herring overnight in water, tea, kvass, or milk. Skin, bone, and chop fine. Fry lightly with a finely chopped onion in 1 spoon butter, transfer to a stoneware bowl, and cool. Add 2 eggs, 2 spoons sour cream, a little black pepper, and ground rusks sufficient to hold the mixture together. Use a teaspoon moistened in boiling water to drop pieces of forcemeat into potato soup.