In a small bowl, mix together 3 tablespoons brown sugar, the peanuts, sesame and coconut.
In a medium pot over high heat, bring the 4 cups of water, potato, ginger and 2 tablespoons brown sugar to a boil. Cook until the sweet potato until fork tender, 5-10 minutes. Add the tāng yuán, and give everything a stir so the tāng yuán doesn’t stick together. Cook the tāng yuán until they float to the top of the soup, 3-5 minutes.