Preheat oven to 400°. Season chicken with salt and pepper. In wide Dutch oven over medium-high heat, warm oil. Working in batches, brown chicken 2-3 minutes per side; transfer to a plate. Add garlic to pan; cook, stirring for 1 minute. Remove pan from heat. Add chicken, spices and zest, stir to combine. Cover pan and place in oven, roast 30 minutes, occasionally basting with pan juices. Transfer chicken to serving platter; leave garlic in pan. Cover chicken loosely with foil. Set pan over medium heat; mash garlic. Add stock and cook, stirring occasionally, for 5 minutes. Whisk in butter a few pieces at a time. Season with salt and pepper. Transfer to a gravy boat and serve with chicken.