In this Middle Eastern-style recipe, plain yogurt plays a double role: First it tenderizes the chicken, then it helps thicken and enrich the sauce. During the summer months, stoke up your barbecue and grill the chicken outdoors. The chicken thighs and coriander sauce can be served hot or at room temperature. The sauce can be made up to 24 hours ahead of time, kept covered in the fridge, but reheat it gently so it doesn't boil and separate. The chicken can marinate up to 24 hours, but broil it at the last minute. Time does not include marination.