Steam the sweet potatoes over rapidly boiling water for 10-20 minutes or until tender when pierced with a fork. Mash the cooked potatoes, then measure about 1 ½ cups of the mashed sweet potatoes. (You may have some left over.) Mix the mashed potatoes with the rice flour. Pour the coconut milk or water, 1 tablespoon at a time into the potato and flour mixture, and knead until a smooth, pliable dough forms.
Scoop out about 1 tablespoon of the dough, and shape it into a small ball, creating a well or hollow space in the center using your thumbs. Place about ¾ to 1 teaspoon of shaved palm sugar in the center of the well. Fold the edges of the dough up over the sugar, and reshape into a ball. Make sure that the sugar does not leak out on any side. Repeat until all the dough is used up. Set aside.
Fill a medium saucepan about halfway with the water. Bring the water to a boil over medium heat, then gently drop the balls into the water, working in batches. Cook for about 3 minutes, or until the balls begin to float to the surface. Scoop the floating rice balls out of the boiling water with a strainer, and shake off the excess water, then roll in the flaked coconut.
Serve warm, at room temperature, or cold from the fridge.