Soup for dessert? Categorically, yes. In China, (and other Asian cultures) tapioca is used in both chilled and warm dessert soups. If you’ve never had it, this sweet potato and tapioca soup is a foolproof recipe and a great place to start. We like to serve this one warm because it adds to the comfort and texture of the dish. Taro can be swapped for the sweet potato, but the color of the sweet potato is too vibrant to pass up.
Bring 6 cups of water to a boil in a large saucepan. Stir in the tapioca pearls and return to a boil. Reduce the heat to maintain a simmer. Cook, stirring occasionally, until the tapioca has turned mostly translucent with just a small dot of white in the center, 12 to 15 minutes. (The timing will depend on brand of tapioca you use so keep an eye on it. Do not let it overcook!) Strain the tapioca in a fine-mesh strainer under cold running water to stop the cooking and to remove the excess starch so that the pearls don’t stick together. The tapioca will continue to turn translucent. Set aside over a bowl to let it drain.
Meanwhile, put the sweet potatoes and 4 cups of water in the pan and bring to a boil. Reduce heat to maintain a simmer. Cook until sweet potatoes are just tender, about 5 minutes. Drain the potatoes and set aside.
Wash out the saucepan, if necessary, and return to medium heat. Add 2 cups of water, the coconut milk, sugar, and salt to the pan and cook until liquids are hot and the sugar and salt dissolve, about 5 minutes. Don’t let it boil. Adjust sweetness as desired. Stir in the vanilla, if using, and return the sweet potatoes and tapioca to the pot. Gently break up any tapioca clumps with a rubber spatula. Serve hot.
Traditionally rock sugar, a.k.a. rock candy, or cakes of palm sugar are used. We use Demerara sugar because it’s more accessible. If you want to give the other sugars a try, crack off pieces of the sugar and add to the warming coconut milk mixture until you’ve reached the desired sweetness.