Mash the garlic, salt, cinnamon, coriander, black pepper, and cumin into a past using a mortar and pestle. Pat the chicken pieces dry. Rub the paste all over. Let marinate, covered and chilled, for 6-8 hours.
Preheat the oven to 400°F. Heat olive oil and butter in a large oven-safe skillet (large enough to accomodate chicken in one layer) over medium-high heat. Brown the chicken pieces on all sides, about 3-4 minutes per side.
Transfer the pan to the oven; bake for 20-30 minutes or until the juices run clear when the leg is pierced with a fork. Remove the chicken from the pan and transfer to a platter. Tent loosely with foil and let rest for 5 minutes before serving.