How to tenderize beef & make the best Beef and Onion Stir-Fry

BEEF AND ONION STIR-FRY

T= tablespoon
t=teaspoon

1lb. Flank steak
1/4 cup water
1 1/2 t baking soda

Marinade:
1/4 t ground white or black pepper
1 T low sodium soy sauce
2 grated garlic cloves
1 t cornstarch

Sauce:
1/2 t sesame oil
1 T Shao Hsing rice cooking wine
1 T oyster sauce
1 T dark soy sauce
1 T sweet chili sauce: https://amzn.to/3SKRl6x OR 1/2 T sugar
1/2 t ground black pepper
3 T brown braising sauce
2 T unsalted beef broth
1/2 T cornstarch

Other ingredients:
2 sweet onions
3 green onions
3 T neutral oil
1/4 t ground black pepper
2 T Shao Hsing rice cooking wine
2 to 4 T water