3 tablespoons commercial sour cream
1 tablespoon plus 1 1/2 teaspoons prepared horseradish
1 tablespoon onion juice
3 tablespoons dry mustard
1 tablespoon cider vinegar
Combine all ingredients in a small mixing bowl, mixing well with a wire whisk.
Spoon mustard into sterilized jars. Cover with metal lids, and screw bands tight. Refrigerate 24 hours before serving. Use in salad dressings or sauces.