4 tablespoons vegetable oil
2 Spanish onions, chopped
3 garlic cloves, chopped
2 tablespoons finely chopped ginger
4 green chiles, chopped
Seeds from 10 cardamom pods
1 tablespoon ground coriander
1 tablespoon paprika
1 tablespoon ground cinnamon
1 tablespoon ground turmeric
2 teaspoons ground cumin
1 teaspoon ground fenugreek
1 teaspoon mustard powder
1 (14 ounce) can chopped tomatoes
1 pint vegetable stock
2 tablespoons lemon juice
Pared rind of 1 lemon

Heat the oil in a heavy pan and fry the onions, garlic and ginger for 5 minutes. Add the chiles and cook for 2 minutes more.

Add the remaining spices then stir for 30 seconds. Stir in the tomatoes, stock, lemon juice and rind. Bring to the boil then simmer uncovered for 30 minutes.

Discard the lemon rind. The sauce is now ready to use or may be kept in the refrigerator for several days.