This is the basis for many of the restaurant-style curries you'll find . The curry recipes use half or two-thirds of the amount that this recipe gives. If you have some left over you could use it in a vegetable curry or freeze it. The recipe doesn't work as well if you try to make a smaller portion. It will keep in good condition in the freezer but only for a few weeks. Remember to wrap it up well or your ice-cream may take on a strange taste!. A. Heat the oil in a heavy pan then add the chopped onion and stir for a few minutes with the heat on high B. Add the ginger, garlic, green chile, turmeric, cumin and coriander. Stir for 30 seconds then put the heat down to very low C. Cook for 20 minutes stirring from time to time making sure nothing browns or burns D. Take off the heat and cool a little. Put 4 fl oz cold water in a blender, add the contents of the pan and whizz until _very_ smooth. Add the passata and stir E. Put the purÚed mixture back into the pan, add the salt and cook for 30 minutes over low heat stirring occasionally to stop it catching on the pan (you can add a little hot water if it gets too dry)