Bake good sour apples and, while still hot, rub them through a fine sieve. For [every] 3 spoons yellow mustard, add 4 spoons sieved apples. Mix together and, for these proportions, add 2 heaping tablespoons sugar. Dilute thoroughly with vinegar boiled with spices as for marinating. Two teaspoons salt may be added. This mustard has an excellent flavor. Let it mellow for at least 3 days before using.