A recipe for making sardellen or herring sauce – Brown a spoon of flour in heated fat, add a quantity of hot fish stock and a few sardellen chopped fine, which you have previously washed in cold water, also a finely-chopped onion. Let this boil a few minutes, add a little vinegar and sugar; strain this sauce through a wire sieve and add a few capers and a wineglass of white wine and let it boil up once again and thicken with the yolk of one egg.