Combine and whisk well together; bourbon, soy, mustard, onions, sugar, salt, Worcestershire, pepper and garlic. Place steaks in a shallow dish and pour marinade over. Cover with plastic wrap and refrigerate overnight. Preheat grill. Season steaks on one side with salt and pepper. Place seasoned side down on grill. Before flipping season top of steaks. Cook to desired temperature.Remove from grill to a serving platter and top each steak with one tablespoon Bourbon Butter.
For Bourbon Butter: Allow butter to come to room temperature. Combine all ingredients in a food processor. and mix well. On a flat surface, form butter mixture into a log about 2 inches in diameter.Roll in parchment paper and freeze. Chips can be sliced as needed.