For the holidays, my dear friend Maria Elena Lynch makes a vat of this addictive mustard, which she gives as presents. It's both tart and sweet, and nothing makes a sandwich taste better.
3-3/4 ounces dry mustard
1 cup cider vinegar
1-1/4 cups sugar
In a double boiler over medium heat, combine ingredients. Cook over simmering water 2-3 hours, or until thick, stirring occasionally. Let cool. Pour into hot, sterilized 4-ounce glass canning jars (leaving headspace). Seal and refrigerate.