Soak the seeds – Combine the yellow and dark mustard seeds in a bowl. Pour in enough water to cover them and let soak for 6–12 hours. Soaking softens the seeds and reduces bitterness.
Drain and blend – Drain any excess water. Transfer the soaked seeds to a food processor or mortar and pestle. Add about 100 ml (slightly under 1/2 cup) of fresh water and pulse until you have a coarse, crunchy mixture. If you prefer a smoother mustard, blend longer.
Season – Add vinegar, sugar (or honey) and salt. Taste and adjust the sweetness or acidity to your liking. (Omitting vinegar entirely yields a milder mustard that some traditionalists prefer)
Optional flavours – Stir in oil for a silkier texture. For a herbaceous note add dried tarragon; a spoonful of whisky or cognac adds warmth.
Mature the mustard – Transfer the mixture to a sterilised jar, cover and refrigerate. Let it sit for at least 12 hours before using; mustard mellows as it rests. Homemade Skåne mustard keeps for up to six months in the refrigerator.
