Slice the beef as thin as you can and add to a large bowl. Mix in the baking soda, a tablespoon of soy sauce, and a teaspoon of cornstarch, along with a splash of water. Let sit for 15 minutes.
In another bowl, whisk together remaining soy sauce, sesame oil, two teaspoons of cornstarch, rice wine vinegar, oyster sauce, and brown sugar.
Place a large sauté pan on high heat. Add in a tablespoon of oil and fry the beef (tossing continuously) for 3-4 minutes, until brown. Remove beef from pan and add in the rest of the oil and the broccoli, along with a cup of water. Cover and steam for 3-4 minutes.
Once broccoli is steamed, uncover and add in garlic and ginger. Cook for one minute, turn heat to low, then add beef and sauce into pan. Stir for 1-2 minutes, or until sauce is thickened. Take off heat and serve, garnished with sesame seeds.