STEAK: Combine first 7 ingredients in a large zip-top plastic bag. Add the steak. Seal and marinate in refrigerator for 8 hours or overnight, turning bag occasionally. Remove steak from bag, saving the marinade for later.

Barbeque the steak on the grill for 5 minutes on each side or until desired degree of doneness. Let stand for 10 minutes, and cut diagonally across grain into thin slices.

Combine marinade and cornstarch in a saucepan. Bring to a boil, cooking 1 minute.

POTATOES: Place the potatoes and garlic in a large dutch oven. Cover with water. Bring to a boil. Reduce heat, simmer 30 minutes or until tender. Drain.

Return potatoes and garlic to a pan and place over medium heat. Add sour cream, milk, butter, salt, and 1/4 TSP pepper. Mash the potatoes mixture to desired consistency with a potato masher. Stir in chopped chives. Mound 3/4 cup potatoes on each plate. Arrange slices of steak alongside. Drizzle 1 tablespoon sauce on each plate. Sprinkle with chive pieces.