Please read blog post for more recipe details.
If you like your broccoli soft, add about 1/4 cup of water to the broccoli while it cooks. It should be absorbed and evaporated off by the time the broccoli is soft.
For the sauce, you can substitute more oyster sauce or hoisin sauce for the other one (use 1/4 cup of hoisin or oyster sauce instead of 2 Tablespoons for each one).
Make the sauce: in medium bowl whisk together the water and cornstarch until smooth. Whisk in the remaining all sauce ingredients (soy sauce, brown sugar, oyster sauce, hoisin sauce, rice vinegar, and sesame seed oil). Set aside.
Stir the sauce one more time to make sure the cornstarch is incorporated, then pour the sauce over the beef and broccoli. Heat the sauce to a strong simmer. Cook for about 1-2 minutes to thicken the sauce, stirring occasionally to make sure all beef and broccoli is coated with sauce.