Cut the meat into thin strips and put them in a bowl. Drizzle a good third of the soy sauce over it, mix and marinate the meat for 30 minutes. In a frying pan (or wok) heat the oil. Sweat the onions, peeled and cut into slices about 5 mm thick, until golden. Add the stiffly beaten egg white mixed with the potato flour to the meat and mix everything together thoroughly. Heat plenty of oil for frying in a 2nd frying pan. Add the meat and fry it in the oil. Be careful that the strips do not stick together. Remove the meat with a slotted spoon and transfer to the other frying pan or wok with the sauteed onions. Mix and then add the rest of the ingredients.
Heat everything together as usual and put the dish hot on the table.