Fanshu Tangshui (Chinese Sweet Potato Ginger Dessert Soup)
A Cantonese tong sui made from four ingredients: sweet potato chunks simmered in a clear ginger and brown sugar slab syrup. Served hot in winter or chilled in summer.
Servings 6 servings
Ingredients
For the Soup
- 2 pounds sweet potatoes Chinese yellow fleshed fanshu preferred, or Japanese satsumaimo, peeled and roll cut into 1 to 1.5 inch chunks
- 2 ounces fresh ginger about a 3 inch piece, unpeeled, smashed and sliced into coins
- 3.5 ounces Chinese brown sugar slab (peen tong) or an equal weight of rock sugar
- 6 cups water
- 1 pinch fine salt
Optional Add Ins
- 8 dried red dates (jujube) slit open, added with the ginger
- ¼ cup cooked ginkgo nuts added in the last 5 minutes
- 1 cup glutinous rice balls (tang yuan) boiled separately and added at the table
Instructions
Prep the Sweet Potato
- Peel the sweet potatoes. Roll cut them into 1 to 1.5 inch chunks by cutting on a diagonal, rolling the potato a quarter turn, and cutting again, so each piece has a flat face and an angled face.
- Drop the chunks into a bowl of cold water and leave them there while you build the syrup. This rinses off loose surface starch and helps keep the finished broth clear.
Build the Ginger Syrup
- Scrub the ginger but do not peel it. Smash the piece with the flat of a knife until it splits open, then slice it into thin coins.
- Combine the ginger, the brown sugar slab and 6 cups of water in a medium pot. Bring to a boil, then reduce to a gentle simmer and cook for 10 minutes, until the sugar slab has fully dissolved.
- Taste the syrup and adjust the sugar now. Aim for slightly under sweet, since the sweet potato will add sweetness of its own.
Simmer and Serve
- Drain the sweet potato and add it to the syrup along with a pinch of salt. Return to a bare simmer, with a bubble breaking only every second or two.
- Simmer gently for 12 to 15 minutes, stirring no more than once or twice, until a paring knife slides into a chunk with only slight resistance. Do not let the pot boil hard or the chunks will break apart and cloud the broth.
- Remove from the heat, cover, and rest for 10 minutes so the chunks finish cooking and soak up the ginger.
- Ladle into small bowls, ginger coins included, and serve hot. To serve it chilled, cool completely and refrigerate at least 4 hours.
Notes
- Keep it clear: rinse the cut chunks, hold a bare simmer instead of a boil, and stir as little as possible. Cloudiness is sweet potato starch escaping into the broth.
- Sweet potato choice: Chinese yellow fleshed fanshu holds its shape best. American orange sweet potato works but is wetter, so cut the pieces slightly larger and pull the pot at 12 minutes.
- Ginger scale: 1 ounce for mild, 2 ounces for standard, 3 ounces for a properly warming bowl.
- Make ahead: keeps 4 days refrigerated and the ginger flavor deepens overnight. It thickens as it sits, so loosen with a splash of hot water when reheating.
- Do not freeze: sweet potato turns grainy and watery after freezing.