Cut the beef into thin slices 2 inches long. Put the slices into a bowl and add the light soy sauce, rice wine or sherry, and cornstarch. Mix well with the beef and allow the mixture to marinate for 15 minutes.
Cut the pepper into 2 inch strips.
Heat a wok or large skillet until it is very hot. Add 1 tablespoon of the peanut oil and when it is almost smoking, stir-fry the beef for 3 minutes. Remove the beef slices and drain them in a colander or sieve.
Clean the wok or pan, add the remaining 1/2 tablespoon of peanut oil and reheat. When it is hot, stir fry the peppers and snow peas for 2 minutes. Then add the chicken stock and dark soy sauce. Bring the mixture to a boil. Return the cooked beef to the pan and give the mixture a few quick stirs to mix it well. Serve immediately.