The oven should be preheated to 200°C/400°F/Gas 6. Scrub the sweet potatoes and slice them into 1cm (⅓in) thick pieces, brush lightly with olive oil and season and place in the bottom of a ceramic roasting dish. Brown the chicken pieces in olive oil, then place the legs only on top of the sweet potatoes and put in the oven for 25 minutes. Meanwhile, make the olive sauce by blending the ingredients in a blender or small food processer until fairly fine but not a purée.
When the 25 minutes are up, remove the dish from the oven, turn the legs over and add the breast pieces before returning to the oven and cooking for a further 20 minutes. Then take it out again, pour the sauce over the chicken and return to the oven until the chicken is cooked. To check, insert a fine knife into the thickest part of the breast: when the fluid runs out clear the meat is done. Serve with a good mixed salad.