1. Chop or mince the beef. Put into a bowl
2. Prepare the marinade: add the salt, sugar, soy sauces, pepper, wine or sherry and potato flour to the beef. Add the water, one spoonful at a time, stirring vigorously in the same direction between additions until too difficult to continue. This makes the beef fluffy and velvety. Leave to marinate for 15 minutes. Blend in the oil.
3. Loosen the rice grains as much as possible.
4. Heat a wok over a high heat until smoke rises. Add 3 tbsp of the oil and swirl it around. Add the garlic and, when it sizzles, add the ginger and the white spring onion. Stir a few times. Add the beef and, sliding the wok scoop or metal spatula to the bottom of the wok, flip and toss, breaking up any lumps at the same time. When partially cooked, splash in the wine or sherry around the side of the wok, continuing to stir as it sizzles. Pour in the beaten egg, tip in the rice, turn and toss for about 2 minutes or until all the ingredients are very hot and well mixed. Stream in the remaining oil around the side of the wok, turning the rice to incorporate it. Remove from the heat.
5. Add half of the lettuce and the green spring onion. Scoop on to a warm serving dish. Top with the remaining lettuce and serve hot.