Mix all ingredients together except the butter. Let it marinate for at least 3 hours (best is overnight).
Once marinated, arrange the chicken pieces in a buttered oven tray.
If you like, sprinkle tandoori powder and put some butter on each piece of chicken.
Cook the chicken in a pre-heated oven 200°C (about 390°F) until it is soft and a little brown on top, about 20 minutes.
Tandoori chicken is best when made on a grill or barbecued. It has this name because it is traditionally cooked in a tandoor oven.