Cut the beef crosswise into 5mm (¼inch) strips and coat with the sesame seeds. Remove the florets from the broccoli stalk. Peel the broccoli stalk to remove the tough outer layer and thinly slice crosswise. Mix all the broccoli with the yellow and red pepper. Combine the beef stock, soy sauce, ginger, cornflour and crushed red chilli.Heat half of the oil in a wok, add the beef and stir fry quickly until brown. Remove with a draining spoon and keep warm. Add the remaining oil to the wok, add the garlic and vegetables and toss together. Cover the wok and cook the vegetables, shaking frequently until almost tender. Stir the stock mixture and pour into the wok, add the beef and any juices that are on the plate. Simmer until the sauce has thickened. Pour onto the serving dish and garnish with chillies and toasted sesame seeds.