A classic Cantonese tongsui famous across China, let Adam Liaw show you how it's done with this sweet and light dessert.
Cantonese desserts are famous across China and sweet soups are classic. I'm making a very, very simple dessert, snow fungus and sweet potato soup. I'm using ginger, sweet potato, goji berries, yellow rock sugar, or you could use normal white sugar, and the star ingredient, white fungus. And just look at how beautiful that is, it's a stunning looking ingredient. To prepare it, you just trim this hard base around the outside there and cut up these pieces into little bits. Now for the sweet potato, you could just cut it into little chunks, but I think this kind of rolling cut where you make an incision and then roll the sweet potato over and make another cut, and another one again, it gives you just a little bit more visual interest. Don't really need to take the skin off ginger, but I think in this case it's probably worthwhile doing. Cut it into some chunks.
So now what I really need to do is get it all into the pot. The first step is to dissolve the rock sugar to form the base of the soup. I don't want to overdo the sugar though because the really important part of a good Tong Sui or sweet soup is that it's not just boiling sugary water. It's about bringing out the natural sweetness of the ingredients themselves. Now in with this amazing white fungus. White fungus doesn't have a strong flavor, but it's prized for its silky, crunchy texture that works perfectly in a soup like this. Then in with some goji berries and just a pinch of salt. I want to keep the heat really low and cook that for anything from 45 minutes to a couple of hours depending on how you like the texture of your potato. But the low heat is so important. Whenever you're cooking a starchy vegetable, keeping the heat low converts the starch to sugar and that gives it its natural sweetness. A classic Cantonese, Tong Sui, sweet potato and white fungus soup.