Chicken Mushroom Cashew Nut Sauce

2 onion
2 tbsp tomato puree
2 oz cashew nuts
1 1/2 tsp garam masala
1 garlic clove, crushed
1 tsp chilli powder
1 tbsp lemon juice
1/4 tsp turmeric
1 tsp salt
1 tbsp low fat natural yogurt
2 tbsp corn oil
1 tbsp chopped fresh coriander
1 tbsp sultanas
1 lb chicken without skin and bone, cubed
6 oz buttom mushrooms
1 1/4 cups water
Sprig of coriander, to garnish

Cut the onions into quarters and place in a food processor or blender and process for about 1 minute.
Add the tomato puree, cashew nuts, garam masala, garlic, chilli powder, lemon juice, turmeric, salt and yogurt to the processed onions.
Process all the ingredients in the food processor for a further 1 minute.
In a saucepan, heat the oil, lower the heat to medium and pour in the spice mixture from the food processor.
Fry the mixture for about 2 minutes, lowering the heat if necessary.
Add the fresh coriander, sultanas and chicken and continue to stir-fry for a further 1 minute.
Add the mushrooms, pour in the water and bring to a simmer. Cover the pan and cook over a low heat for about 10 minutes. Check that the chicken is thoroughly cooked and the sauce is thick. Cook longer if necessary.
Serve the chicken garnished with a sprig of coriander.