Trim any excess fat from the beef then slice as thinly as possible.Tip: To get the beef as thin and tender as many restaurants, par-freeze the beef so it can be cut thinner. After slicing use a meat mallet to flatten each small piece of meat.
Peel and/or seed the onion, bell pepper, and carrot, then slice into equally sized strips. Finely mince the garlic.
Black Bean Sauce
In the small bowl combine the black bean sauce, dark soy sauce, beef stock, and sugar. In a cup whisk the cornstarch and water together with a fork.
To Cook
Place the wok over high heat. When hot add the peanut and sesame oil then swirl to cover the bottom of the wok.
Add the beef and cook while stirring until it loses its redness. Add the onions, bell peppers, and carrots. When the onions start to become translucent add the garlic and stir through.
Immediately add the black bean sauce and stir through. When it starts to boil add the cornstarch mix while continuing to stir. As soon as it is thickened and starts to boil again serve.