Soak: Combine the mustard seeds, cold water and white wine vinegar in a clean sterilised glass jar. Cover and refrigerate for 24 hours.
Blend: Transfer everything to a blender. Add the salt, then blend until smooth or slightly grainy.
Adjust: Add cold water gradually until you reach your preferred consistency. You may not need all 60 ml.
Mature: Transfer to a clean, airtight jar and refrigerate for 2–3 days to develop the flavour. Keeps for about 1-2 months.
