Prepare the ingredients. Peel the sweet potatoes, slice them thinly, and steam until soft. Weigh the tapioca pearls and grind them into a fine powder.

Divide the powdered tapioca in half. Add half of the powdered sugar and the hot water to the tapioca, then mix well until a smooth dough forms.

Place the steamed sweet potatoes in a blender with the remaining powdered sugar, coconut milk, and heavy cream. Blend until smooth. Transfer to a pan and cook over low heat, stirring, until it forms a smooth, cohesive paste.

Let the sweet potato filling cool, then roll into balls. Flatten the tapioca dough, place the sweet potato ball in the center, and wrap the dough around it. Press into a mooncake mold if desired. Place the mooncakes on parchment paper for steaming.

Steam the mooncakes for about 20 minutes, or until they turn translucent. These mooncakes are best enjoyed warm. If they cool and become dry, re-steam to soften.