Prepare a medium fire. Gently peel back corn husks, leaving attached at base. Remove silk. In food processor, combine butter, scallions, garlic, chili powder, and lemon juice. Process until well blended. Rub 2t of this butter over each ear of corn. Fold husks back over; tie with string; soak corn in a lg bowl of cold water 10 mins to prevent burning. Squeeze out excess water. Place damp corn on an oiled grill set 4-6" from coals. Grill, turning and moving ears frequently, until outside leaves are lightly charred. Peel off husks and serve with additional chili butter.