Cut the beef steak into 1cm wide strips. Marinate with all the marinating seasonings for 15 minutes. Add cornstarch and mix well. Then add sesame oil just before frying.
Add cooking oil in a large pan until the oil can evenly cover the bottom of the pan. spread the beef strips in. Let them stay for around 10 seconds and gently stir them several times until the beef strips change color. Transfer the beef out and leave around 1 tablespoon of the oil in.
Add doubanjiang and fry until the oil turns red, add garlic and ginger in. Fry for 1 minute until almost cooked.
Return the beef strips in. Add around 1 tablespoon of light soy sauce and mix well.
Notes
If you cannot find baby ginger, you can choose tender old ginger. But only 1/2 of the amount needed.