Rinse the pak choi leaves under cold running water and pat dry. Remove the tough outer leaves. Cut the rest into narrow strips.
Heat the oil in a wok. Carefully add the leaf strips in portions and deep-fry for about 30 seconds until they collapse and become crispy. Drain on kitchen paper.
Put the salt, sugar and pine nuts in a large bowl, then add the fried pak choi. Mix briefly once and serve immediately.