Bring a large pan of water to the boil, then add the 2 tablespoons salt and a few drops of vegetable oil and blanch the cabbage for about 1 minute. Drain and put to one side.
Heat a wok, add a little vegetable oil and stir-fry all the mushrooms until they are soft and giving off a little liquid.
Add the oyster sauce, sugar and a pinch of salt and cont