On a cutting board, mince together garlic, brown sugar, and salt until almost forming a paste. Transfer to a small bowl; stir in hot sauce.
Rub this mixture evenly on both sides of the steaks. Let stand for 20 minutes.
Coat grill rack with nonstick cooking spray. Preheat grill to high (400-450 degrees F). Grill steaks for 5 minutes per side for medium-rare. Adjust your cooking time per side for other than medium-rare.
Transfer steaks to a cutting board; let stand for 3 minutes. Cut each steak in half; top each half with 1 teaspoon of butter, and serve.