Grind the mustard seeds into mustard flour. They get a little coarser in a mortar and a little finer in an electronic coffee grinder. Alternatively, you can use purchased mustard flour. Add all other ingredients and puree. Let it steep in the refrigerator for at least 4 hours, stirring occasionally.
Then fill into sterile screw jars and store in a cool place.
The amount is enough for 2 glasses of 190 ml each. It will keep in the refrigerator for approx. 6 months.