Grandpa's Finnish Christmas Mustard

Description
The recipe also says to experiment and add a little cognac or whiskey.

Ingredients

 * ½ cup Coleman's dry mustard
 * ½ cup sugar
 * 2½ tablespoons potato starch (I often substitute corn starch for potato starch)
 * ½ cup cream
 * 1 – 4 tablespoons apple cider vinegar

Directions

 * 1) Mix the dry ingredients together and sift into a heavy bottomed kettle.
 * 2) Add the cream and mix well.
 * 3) Heat over a medium heat, stirring and scraping the bottom constantly until it bubbles and starts to thicken.
 * 4) Take the pan off the heat and add at least a tablespoon of vinegar.
 * 5) You can add more if you like, the vinegar makes the mustard more sour and a thinner consistency.
 * 6) Put the mustard in a bottle while warm.
 * 7) Keep in the mustard in the refrigerator.
 * 8) Warning: do not let the sauce boil because the potato (or corn) starch will thicken and become like glue!