Crush mustard seed using a mortar and pestle for a few seconds.
Slowly add water and continue grinding the seed. Use hot water for a milder mustard and cold water for a spicier mustard. Grind until the water is incorporated, leaving some seeds whole.
Add the remaining ingredients and continue grinding until the desired consistency is achieved. Store the mustard in a glass jar in the refrigerator for 24 hours before serving.
Mustard will keep for up to one year in refrigerator.