In my family, this mustard sauce is as essential as the ham on the holiday table. It takes no time to whisk together, and it is so nice to have on hand for leftover ham sandwiches.  Not all dry mustards are created equally, and depending on the type you use, your sauce could taste unpleasantly strong. I don't have a strong preference of brands here, but in recent years I use the Tone's ground mustard, which I find at my local co-op.