"From "The Cooking of the British Isles" by Adrian Bailey."
236.59 ml fish stock or 236.59 ml beef stock or 236.59 ml
lamb stock, depending on the food with which it is to be served
( and cut into halves if large)
fresh ground black pepper
In a heavy 8 to 10-inch skillet, melt the butter over moderate heat. When the foam begins to subside, stir in the flour and mix thoroughly. Pour in the stock and, stirring constantly with a whisk, cook over high heat until the sauce thickens and comes to a boil.
Reduce the heat to low and simmer the sauce for about 3 minutes to remove any taste of raw flour. Then stir in the capers, vinegar, salt and a few grindings of pepper. Taste for seasoning and serve hot from a small bowl or a sauceboat.