Slice the beef VERY thinly across the grain at an angle.
Combine the ingredients for Bowl 1 in a medium size bowl. Add the beef slices. Toss. Let stand at room temperature for 1 hour. Alternatively, you can marinate for several hours refrigerated.
In the meantime, combine the ingredients for Bowl 2 in a medium bowl or measuring cup, whisk together and leave the whisk in the bowl, set aside.
Heat the wok or heavy based fry pan to HIGH add 2 Tbs. of the vegetable oil.
Stir-fry the marinated beef until lightly brown (1-2 minutes). The meat should be very rare and raw in places. Remove with a slotted spoon, place in a bowl, set aside.
Add the last Tbs. of the oil to the wok and add the garlic and broccoli, stir-fry for 1 minute, add 3 Tbs. of water and toss often for 2 minutes, the water will evaporate but the broccoli will still be crunchy.
Whisk the contents of Bowl 2 and add to the hot wok, let it heat and bubble for a minute or so. Add the beef back to the pan, toss and, allow the mixture to bubble and thicken. Cook for another minute or so.
Empty to a serving dish and sprinkle with chili flakes if desired.