Homemade Mustard

Mix all ingredients except egg yolks and allow to stand two hours. Whisk yolks into mixture then transfer to top of a double boiler. Cook over hot, not boiling, water and stir constantly until mustard thickens. (Approximately 5 minutes.) Cool mustard and cover. Refrigerate up to 1 month. Yields 1 cup. NOTE: For tarragon mustard, add 1/2 teaspoon crushed dried tarragon when adding egg yolks. For lemon or lime mustard, add 3/4 teaspoon grated lemon or lime peel, and 1-1/2 teaspoon lemon or lime juice when adding egg yolks.