Blanch the Chinese cabbage leaves in boiling hot water for 30 seconds. Drain, wash under cold running water and drain again thoroughly.
Heat the oil in the preheated wok and add the Chinese cabbage, leek and garlic. Sauté for 2-3 min.
Add the clear soup and soy sauce, turn the temperature down low, cover and simmer on low heat for 10 min.
Remove the vegetables from the wok with a wok turner and set aside. Bring the clear soup to a boil and reduce violently until reduced by half.
Mix the cornstarch with the water, then stir into the wok. Bring to a boil and cook, stirring throughout, until the sauce thickens and becomes clear.
Lower the heat, stir in the vegetables, and stir in the whipping cream or yogurt. Simmer gently over moderate heat for 1 minute.
Transfer to a serving dish, sprinkle with the chopped cilantro and bring to the table.
A dollop of whipped cream, but you can omit the whipped cream.