Place steak in shallow glass dish. Scatter onions on top and underneath
steak. Mix remaining ingredients; pour over steak. Cover dish with plastic wrap
and refrigerate at least eight hours, but preferably overnight, turning steak
Remove steak from marinade. Grill steak on barbecue grill or under broiler
until preferred doneness is reached. At the same time, heat up marinade with
onions, letting it simmer until onions are semi-soft.
To serve: Cut meat diagonally across the grain into very thin slices; serve
with onions and marinade.
This marinade is also excellent using chicken or thick pork chops instead of
the flank steak. Discard unused marinade.