Preparation Combine the sweet mustard and 2 tablespoons of the Dijon mustard in a medium bowl. Add the sugar and 1 tablespoon of the vinegar. Gradually add the oil, whisking constantly. Adjust the flavors as necessary. The sauce should be neither overly sweet nor overly acidic. Add a little water if the sauce gets too thick. Stir in the chopped dill. It will keep, refrigerated, for 2 to 3 weeks.