Heat oven to 400°F Put ½ a lemon and ½ a garlic head into the chicken's cavity, then put into a roasting tray. Mix butter, garlic and half the spices and spread over chicken breast and legs. Season well. Can be prepared up to a day ahead and kept covered in the fridge. Put the remaining garlic into the tray and roast chicken for 1 hours Mix remaining spices into yogurt and season.