Steam the lemon without breaking. When cool, wipe out the water. Cut each lemon into 8 pieces. Steam the chillies and the garlic.
Heat oil and season with mustard and fenugreek. Sauté with ginger. Add water, vinegar, salt and sugar. When it boils, remove from fire. When it is still warm, add the lemon pieces, salt, pepper corns (as a bunch), chillies and garlic. Stir well and store in a mud vessel.