Cut the beef into thin slices against the grain (which means at 90 degrees to the direction of the fibres in the meat).
Place beef in slow cooker.
Mix the corn flour with the water, then add to the slow cooker.
Add the Sauce ingredients to the slow cooker.
Cook on HIGH for 3 hours (or pressure cook on high for 40 minutes).
TO SERVE IMMEDIATELY
Steam or boil broccoli until "tender crisp" (just cooked, still bright green and still crisp).
Add to beef and sauce, toss to combine. Serve over rice.
TO MAKE AHEAD TO FREEZE (2 MONTHS) OR REFRIGERATE (2 DAYS)
Let the beef and sauce cool.
Meanwhile, blanch the broccoli very briefly, then run under cold water or plunge into ice water to stop from cooking further.
Drain broccoli, then combine with the beef and sauce.
Place into ziplock bags or airtight containers and freeze or refrigerate.
To cook, thaw then reheat in the microwave, covered. Be careful not to heat for too long because otherwise the broccoli will overcook.
Serve with rice.