What is choy sum?
This beautifully leafy green is available at all Chinese supermarkets year-round, and if you have a local Asian community, you might find it at your local farmer's market too. Sometimes, it's alternatively labeled 油菜 "yu choy".
The flavor is sweet and delicate, and the texture is similar to bok choy, lighter than other heartier vegetables.
Its appearance is a bit similar to gai lan. How do you differentiate between them? Choy sum is a lighter, brighter green compared to gai lan's dark, almost blue-green leaves.
The stems are quite different as well; choy sum stems are curved and rather flexible, while gai lan stems are round and dense, like broccoli.
Stir-fries that involve heartier vegetables often call for blanching as a pre-cooking stage. Blanching a hearty vegetable ensures that it's tender enough for a pleasant eating experience.
Choy sum, however, is tender enough to stir-fry straight from raw (after washing and trimming, of course). In Cantonese cooking, this is called 生炒 (saang1 caau2). No pre-cooking necessary!