Tang yuan (汤圆, literally round soup — referring to the round shape and the soup in which they are served) are glutinous rice flour balls traditionally eaten during the Lantern Festival (Yuan Xiao Jie, 元宵节, the 15th day of the first lunar month) and at the Winter Solstice festival. They come in two main forms: filled tang yuan (with a sweet, semi-liquid filling of sesame paste, peanut paste, or red bean paste) and plain tang yuan (unfilled, smaller, eaten in a sweet ginger broth). The experience of eating a filled tang yuan — the smooth, slightly chewy glutinous exterior and the burst of warm, sweet, slightly oily filling — is one of the quintessential Chinese sweet food pleasures.
The glutinous rice dough: 200g glutinous rice flour + 120-130ml warm water. Knead until smooth. The dough should be soft, non-sticky, and pliable. If it tears when stretched, add more water. If it sticks, add more flour. Filled tang yuan (sesame paste): The sesame filling: 100g ground black sesame seeds, toasted, mixed with 60g icing sugar and 40g melted lard. Mix until combined. Refrigerate until firm. Roll into small balls (10g each). Shaping: Take approximately 20g of dough. Flatten into a circle. Place the filling in the center. Gather the dough around the filling and seal, rolling into a smooth ball. Cooking: Bring a large pot of water to a boil. Add the tang yuan. When they float to the surface (3-5 minutes), they are cooked. The skin should be translucent and slightly puffed. Serve in plain water (with brown sugar syrup), sweet ginger broth, or sweet osmanthus (gui hua) syrup.
Eileen Yin-Fei Lo, Mastering the Art of Chinese Cooking (2009); Fuchsia Dunlop, Every Grain of Rice (2012)