Chicken and Yoghurt Curry

(I got this fantastic recipe from Kek!)

Serves 6

2 pounds chicken pieces
1 medium onion, roughly chopped
3 cloves garlic, peeled
1 tsp chopped ginger
½ cup chopped coriander leaves
1 tbs peanut oil
1 tsp ground turmeric
1 ½ tsp garam masala
1 ½ tsp salt
½ tsp chilli powder (optional)
½ cup low fat yoghurt
2 ripe tomatoes, diced
extra chopped coriander to garnish

Blend onion, garlic, ginger and fresh coriander in a blender or food processor until smooth. Heat oil in a heavy saucepan and fry the blended mixture, stirring, for about 5 minutes. Add turmeric, garam masala, salt and chilli powder and fry for a further minute. Stir in yoghurt and tomatoes and fry until liquid dries up and the mixture is the consistency of a thick puree. Add chicken pieces, turning them in the mixture to coat, then turn heat low, cover tightly and cook until chicken is tender (about 30-45 minutes, depending on the size of the pieces). If liquid from the chicken has not evaporated by this time, uncover and raise the heat to dry off excess liquid. Stir gently at base of pan to prevent burning. Garnish with chopped coriander.