Finely grind the mustard seeds in a blender. Add the water, mix until combined, and let soak briefly. Add both varities of vinegar, the salt, and the sugar to a pot. Heat the mixture, then remove from the heat and stir it into the mustard mixture.
Gradually incorporate the oil, a drop at a time, until the oil is completely absorbed. Crush the parlsey in a mortar until smooth, then stir into the mustard. Place the mustard in screw top jars. Place the mustard in a cool place.