Place the chicken in a mixing bowl. Add the yogurt and half the garlic, salt, and pepper. Cover and let stand two hours, turning the pieces in the liquid.
Melt the butter in a heavy casserole and add the oil and onion. Cook, stirring, until the onion starts to brown.
Add the remaining garlic and the spices and cook over low heat, stirring frequently, about two minutes.
Add the chicken and marinating liquid. If necessary, add salt and pepper. Cover and simmer until the chicken is fork tender. (Approximately, 90 to 120 minutes. Serve with rice.