An adaptation from curryfrenzy.com that works - this is the base sauce for many of the curries I will be posting over the next few weeks. This sauce will freeze so multiply it up and freeze down for quick curries.
Fry the onions in the oil on a medium heat until the onions are soft and translucent (5mins).
Add garlic and saute for 1 minute.
add Tomatoes and cook for a further 3 minutes.
Add half the water and simmer for 5 minutes then add the rest of the water and spices. Stir in well and simmer for a further 5 minutes. Keep stirring regularly throughout cooking. Take the pan off the heat and leave to cool slightly before pureeing in a food processor.