Put the sirloin cubes in a shallow glass or ceramic dish. Whisk the cooled liquid ghee, 1 tablespoon cider vinegar and garlic powder in a measuring cup. Pour over the beef and turn the cubes until all sides are coated. Cover and refrigerate for 2 to 3 hours.

Heat an outdoor grill or a Le Creuset Artichaut enameled cast-iron grill pan to medium. Thread the sirloin onto skewers without packing the cubes tightly together.

Grill, turning so the pieces color on several sides. Check a thicker cube with a food thermometer: whole-cut beef should reach 145°F (63°C), followed by a 3-minute rest off the heat. Set the kabobs aside during that rest.