Place the beef strips and cornstarch in a large, resealable baggie and shake to coat.
Cook the beef at 390 in a preheated air fryer for 5 minutes, flip, and cook for another 5 minutes.
While the beef is cooking, mix all the sauce ingredients in a saucepan and bring them to a boil, stirring constantly.
Reduce the heat and simmer until thickened. Add an additional teaspoon of cornstarch if the sauce is too thin.
Mix the beef and sauce ina large bowl and let it sit until the sauce thickens further. Enjoy!
Notes
Storage
Refrigerate leftovers in an airtight container for up to 4 days.
For longer storage, freeze the beef for up to 3 months in an airtight, freezer-safe container.
To reheat, defrost the beef if frozen. Then, add it to a saucepan with a bit of water and cook on medium-low until heated through.
Choosing Beef
Look for flank steak that is bright red, not dull or gray.
This dish cooks quickly, so choose the leanest flank steak possible. You don't need marbling to get it tender when you cut it against the grain.
General Tips
Always preheat your air fryer for even cooking and precise cooking times. You'll always get a better final product, and it only takes a few minutes.
We mentioned this earlier, but it bears repeating. ALWAYS cut your flank steak against the grain. If you cut with the grain, it will NEVER get tender.
You can spray your meats with cooking spray when you air fry, but never spray your air fryer basket directly with nonstick spray. It can damage the coating over time.