The leaves of pak choi should be dark green and the stalks should be rigid and white (though you can find green-stalked pak choi on occasion). The stems should be firm to the touch with no limp leaves. Once brought, store in the fridge for up to a week.
Young pak choi is well worth seeking out; the leaves are more tender and can be enjoyed raw in salads or as a garnish.
Pak choi is a kind of 2-in-1 plant – the dark, thin leaves that sprout at the top cook very quickly and are akin to spinach in consistency. The thicker stalk is firm, crunchy and refreshing. For this reason, it can be tricky to judge the cooking time of pak choi – a good option is to separate the leaves from the stalks and cook the stalks for a couple of minutes, adding the leaves in the last few seconds to wilt down.
Blanching, stir-frying and steaming are all excellent methods for cooking pak choi, as the flavours are retained nicely. Be careful not to overcook or you will lose that refreshing crunch from the stalk which makes a great contrast to rich, sticky, sweet-and-sour dishes. Though usually make from napa cabbage, kimchi, the Korean dish of fermented cabbage, can also be made with pak choi.
If you want to prepare the pak choi in advance, you can blanch in boiling salted water for 1 minute then refresh and dry before sautéing in a frying pan just before serving, as Alan Murchison does in his pigeon recipe. Refreshing the pak choi in iced water is a necessary step to halt the cooking process and maintain the bright green colour of the leaves.
A nice easy way of preparing pak choi is to cook in boiling water or broth for a total of 3 minutes, as Geoffrey Smeddle does in his recipe – cooking in a flavoured broth or stock will help impart flavour into the leaves.