Cut your flank steak into medium or ¼-inch slices. Once cut, put the meat into a room-temperature water bath to rinse out the myoglobin.
Peel and thinly slice the yellow onion into ¼-inch thickness.
In a medium-sized bowl, mix the baking soda, cornstarch, oyster sauce, soy sauce, tamari, white pepper, water, cooking wine, sugar, and mix until everything is incorporated and smooth.
Drain the meat from the water bath, squeeze out the excess water. Add the meat into the marinade and mix until the meat is fully coated in the marinade and set it aside.
Prepare the rice noodles by separating the noodles if you see them stuck together.
In a small bowl, mix tamari, soy sauce, and oyster sauce. Once mixed, set it aside.
Add cooking oil to the marinated beef to seal the juices in the beef.
Fry the yellow onion and the white parts of the scallions for 20 to 30 seconds or until fragrant.
Add the beef and mix. Let everything cook together for 1 more minute. Turn off the heat and add the sesame oil.
Taste to adjust the flavors and plate once it's to your taste! This is usually served at the center of the table and everyone can take the amount they want.
