Whole Spice shares this recipe for homemade mustard from customer George Vierra.

Ingredients
7 cups ground yellow mustard (1 1/2 lb.)
1⁄2 cup brown mustard seed (3 oz.)
1⁄2 cup 1-1/2 cups  yellow mustard seed (2 1/3 oz.)
8 cups white vinegar (prefer Vilux French Champagne Vinegar (6% acidity*) orBeaufort Reims Champagne Vinegar or Poni White Wine Vinegar, Note: Don’t use higher acidity vinegar as it will make the mustard too tart
8 cups white wine (1 bottle of sweet Moscato di Canelliand and 1 1/2bottles of Chardonnay are recommended.
25 garlic cloves, peeled and lightly molested
2 medium sized onions, peeled and chopped
17 bay leaves
65 whole allspice
16 tsp. salt
16 tsp. sugar
16 tsp. dried tarragon

Directions
Mix the first three ingredients well together in an 8-quart pan, and set aside. Add the rest of the ingredients to a pot and bring to boil. Boil until reduced to half volume. Note…this is very pungent! Open windows, turn on fans, etc. Pour the reduced liquid through a strainer. Discard solids. Pour the strained liquid into the mustard pan. Put this pan over low heat and stir constantly for 10 or 15 minutes, until thick.

Pack in sterilized jars. Store in icebox. Fills ten 8-0z. (1 cup) jars.  Can keep refrigerated for up to 3 years. Ages and changes nicely. Can change heat level by varying portions of powder and seeds. Seeds are hotter than ground mustard and brown seeds hotter than yellow.

– George Vierra Mustard July 13, 2015