Heat 60ml sunflower oil in a large saucepan until hot. Add 1 tablespoon black mustard seeds, 1 tablespoon turmeric, 2 tablespoons cumin and 2 teaspoons chilli powder. Cook, stirring, for 5 minutes to release the flavours.
Add ¼ cup peeled, grated fresh ginger, 4 crushed garlic cloves, 1 seeded, finely chopped green chilli and 30ml of malt vinegar and cook for 5 minutes.
Add two 400g cans diced tomatoes, ⅓ cup brown sugar, 1 teaspoon salt and 130ml malt vinegar and simmer for 1-1 ½ hours.
The kasundi is ready when the oil comes to the top.
