Butter or even heavy cream usually gives butter chicken its rich, satisfying quality. In this healthy version of a butter chicken recipe, cashew butter creates an equally luxurious texture. Chickpea flour thickens the sauce, but is optional if you don't have it on hand. For weeknight speed, marinate the chicken ahead of time and you can have this dish on the table in about 30 minutes. Serve with steamed spinach and basmati rice.