In a processor blend 1-1/2 cups plain yogurt with the next 9 ingredients (the lemon juice to cayenne pepper) until smooth and well blended; transfer to a large bowl; mix in the remaining 1 cup yogurt with a wooden spoon.
Add in the chicken and toss to coat.
Cover and refrigerate over night.
Prepare the grill to a medium-high heat.
Place the marinated-coated chicken on the grill, do not wash off the yogurt marinade, but discard any marinade from the bowl.
Grill the chicken (about 12-13 minutes per side) basting with melted butter the last 5 minutes of cooking on both sides, season with more salt and pepper if desired while cooking.