Orange Beef

1-1/2 - 2 lbs. petite sirloin, sliced thinly while still partially frozen.  Marinate in sauce for a while and then stir fry in a bit of oil (save sauce)

Sauce:
2-3 tsp. grated orange zest
1/2 cup fresh orange juice
1/4 cup brown sugar
2 Tbl. rice vinegar
2 Tbl. soy sauce
2 tsp. fresh-pressed or grated ginger

While frying marinated meat, combine 2 tsp. cornstarch with a 3 Tbl. water. And cornstarch mixture to remaining marinade.  Whisk together.  Add sauce to meat in pan.  Stir to combine and thicken. Sprinkle with sesame seeds, if desired.  Serve over rice or noodles.