1. FREEZE CHOPS Pat chops dry with paper towels and rub with salt. Arrange on wire rack set inside rimmed baking sheet and freeze until chops are firm, at least 30 minutes but no more than 1 hour. Combine 2 tablespoons butter, brown sugar, and pepper in small bowl; set aside. Mix remaining butter, chives, mustard, and zest in another small bowl and refrigerate until firm, about 15 -minutes. (Butter-chive mixture can be refrigerated, covered, for 1 day.)

2. GRILL CHOPS Pat chops dry with paper towels. Spread softened butter-sugar mixture evenly over both sides of each chop. Grill, covered, over hot fire until well browned and meat registers 145 degrees, 3 to 4 minutes per side. Transfer chops to platter and top with chilled butter-chive mixture. Tent with foil and let rest 5 minutes. Serve.