Rinse the mustard seeds thoroughly under cold running water.
Bring a pan of water to the boil and blanch the seeds for 2 minutes.
Drain and repeat twice more to reduce the bitterness.
Place the blanched seeds in a pan with the water, vinegar, sugar and dashi.
Blitz the black garlic with a small amount of the cooking liquid to form a smooth paste, then add to the pan along with the black food colouring.
Bring to the boil, then reduce the heat and simmer gently for 30–40 minutes until the seeds are fully cooked and have developed a caviar-like texture.
Check regularly and add a little water if needed.
Allow to cool in the cooking liquid so the flavours can fully infuse.
Store in a clean, sealed jar in the refrigerator.
Drain any excess liquid before serving.
