Grease the base of a small bamboo steamer with groundnut oil and place the pancakes inside. Place over a small pan of boiling water (making sure the water does not touch the base of the steamer), cover and steam for 5-6 minutes. Take off the heat and keep warm, covered in the steamer until ready to serve.
For the filling, heat a wok until smoking and add two tablespoons of the groundnut oil, then add the beaten egg and scramble for one minute, or until cooked through. Transfer to a plate and put to one side.
Return the wok to the heat and add the remaining groundnut oil, followed by the garlic (if using) and ginger. Stir fry for a few seconds to release the aromas, then add the beansprouts, peppers, sweetcorn and mushrooms and cook for 3-4 minutes, or until the vegetables are tender but still with a bit of bite.
Return the egg to the wok and season with soy sauce, sesame oil and white pepper. Add the sliced honey roast ham, if using, and toss for one minute to heat through. Transfer the filling mixture to a large plate and garnish with pickled red cabbage.
To serve, place the plate of filling in the centre of the table together with the pancakes in the steamer. To eat, fold the pancake in half and then half again to give a fanned conical shape, stuff the open end of the pancake cone with the vegetable filling and then eat immediately.