3 tbsp. vegetable oil
6 tbsp. red wine vinegar
1 tsp. salt
1/2 tsp. pepper
1 med. onion, sliced thin
1 (3/4 inch) thick flank steak

Mix all ingredients in order listed, except steak. Trim all fat from beef. Put steak in large, shallow pan. Pour marinade over meat, making sure some dribbles under meat. Cover with foil. After 45 minutes to 1 hour, turn meat and remix marinade.

If necessary to marinate more than 2 hours, refrigerate, turning each hour. Cook to medium rare over grill according to grill directions.