Cut the onion into wedges.

Put beef with ● marinade in a bowl, and rub in. Let it sit for 30 minutes in the fridge.

Mix ☆ sauce ingredients in a different bowl.

Heat oil in a pan and stir-fry the onion over medium heat. Transfer the onion on a plate.

Add more vegetable oil to the pan, and stir-fry the beef and separate it. Once it's cooked, return the onion to the pan.

Pour in the sauce from Step 3, turn the heat up to high, then stir-fry briefly, coating them with the sauce.

Serve on a plate.