Heat oil in a large pot and fry chicken until golden brown. Spoon out and set aside.
In the same pot fry onions, garlic and ginger for a few minutes. Stir in all the spices.
Add tomatoes, tomato paste and water and simmer for a few minutes.
Add chicken, potatoes and salt to sauce and simmer over a low heat for 30 minutes or until the chicken and potatoes are cooked.
Stir in the buttermilk and serve with small portions of brown rice. Garnish with fresh coriander.
When cooking rice, make sure you only use ½ tsp salt in the water per cup of uncooked rice.
For a milder curry, add 2 apples, cubed and replace chilli powder with mild curry powder.