Lay flank steak out on a LG cutting board. Pound out with a mallet until between 1/4 and 1/2 inches thick.

Combine all marinade ingredients. This is a large batch, and can be frozen and used again.

Place steak in a large zip lock bag. Add 1 1/2 to 2 cups of marinade. Remove as much air as possible. Seal and let sit overnight.

Remove from marinade. Roll up and tie every 2 inches with butchers twine. Cut in between the ties.

Heat a pan on low heat. Melt butter. Add sliced onions. Saute for 25 to 35 minutes stir often. 5 minutes before onions are done, add garlic and sherry. Deglaze pan and let liquid completely reduce.

Meanwhile, heat a pan with 1 tbs oil over medium high heat. Place rolls in on end. fry 5 to 7 minutes on each side or until browned well. After browned on both sides, reduce heat to medium. Add 1/4 cup sherry. Cover and steam until liquid is gone. Turn over and repeat. Meat should come out rare. If you like it more done add a little more liquid and cook longer per side.

Remove and let rest tented with foil for 5 minutes. Plate rolls. Add carmelized onion. Serve immediately. Enjoy.