When people think of sweet potatoes, they are probably picturing the hard, yellow- to orange-fleshed tubers that are so hearty, delicious and warming during the winter months. But in season now are sweet potato vines and leaves, which, because they wilt quickly, are rarely exported - the ones you find in the wet markets are almost certainly grown on farms in the New Territories and the mainland.
Both the vines and leaves can be tough if overgrown, so choose the smaller specimens. The leaves are medium-green, broad and pointed at the end; while the vines are long and slender, and often have small, curly tendrils growing off them.
The leaves don't take long to cook and can be stir-fried whole or julienned and added to soup. They're delicious prepared in the same way as water spinach: heat oil in a wok, add half a clove of garlic and stir-fry for a few seconds. Mash a small chunk of belacan (fermented shrimp paste) and add it to the wok (turn on the extractor fan, because this part is smelly). Add the sweet potato leaves and a little salt and pepper, then stir-fry until slightly wilted. Stir in a splash of water or unsalted chicken stock, then cook over high heat until all the leaves are wilted.
If the sweet potato vines are very long, cut them into lengths of about 12cm. Heat oil in a wok and when it's hot, add chopped garlic. Stir-fry until fragrant then add the vine leaves and mix. Add some unsalted chicken stock to the wok, stir again then cover with the lid and simmer for a few minutes. Add a little fish sauce, some salt and pepper then check to see if the vines are tender enough. When they're ready, add some rendered chicken fat (preferably) or a drizzle of sesame oil, stir again, then serve.