Sweet Potato and Old Ginger Soup
番薯糖水·(faan syu tong sui)
Tong Sui: Nostalgic Sweet Endings
A bruised knob of old ginger sits on the cutting board. A sweet potato is peeled. Golden slabs of rock sugar wait for the pot. Thirty minutes on a Tuesday night back burner turns these raw ingredients into a hot bowl of tong sui. The soup is built on their sheer simplicity, but technique defines it: you don't neatly slice the potato, you pry it; you don't just boil the ginger, you smash it and fry it. These quiet motions unlock a golden, crystal-clear broth. Listen to the spoon clinking, drink it while it is hot, and let the ginger clear the day from your throat.
Ingredients
- Jewel or Garnet yams1 1/2 lb
- old ginger2 inch
- peanut oil1/2 tsp
- cold water6 cup
- Chinese brown rock candy3 oz
- kosher salt1 pinch
Method
- 01
Pry the sweet potatoes into jagged chunks.
Wedge the heel of a heavy knife or cleaver a third of the way into the peeled sweet potato and twist your wrist to snap the chunk off, creating irregular two-inch pieces that will absorb the ginger syrup beautifully without turning to mush.
- 02
Soak the sweet potato chunks in cold water to leach out the surface starch.
Submerge the jagged pieces in a bowl of cold water for twenty minutes, then drain and rinse until the water runs clear, which guarantees a brilliant, refreshing broth rather than a cloudy stew.
- 03
Smash the ginger violently to release its essential oils.
Lay the unpeeled ginger on your cutting board and use the flat, broad side of a cleaver to smash it until it splits open and flattens out.
- 04
Dry-fry the smashed ginger and sweet potatoes to lock in their structure.
Heat the oil in a heavy-bottomed pot over medium heat, fry the ginger for a minute until fiercely aromatic, then toss in the drained sweet potatoes for a few minutes until their exteriors are dry and slightly toasted.
- 05
Boil the soup until the sweet potatoes are tender.
Pour in the cold water, bring to a rolling boil, then reduce the heat to medium-low and simmer partially covered for fifteen to twenty minutes until the potatoes are tender but still holding their shape.
- 06
Dissolve the sugar and salt into the finished soup.
Never add sugar at the beginning of the cook; only once the potatoes are tender should you drop in the rock candy and salt, stirring gently for a few minutes until perfectly dissolved and ready to serve.
Notes
If you cannot find Chinese brown rock candy, do not substitute white granulated sugar.
White sugar will render the soup painfully sweet and one-dimensional. Substitute with a half cup of tightly packed dark brown or muscovado sugar to replicate the required caramel and molasses notes.