Mix mooncake dough ingredients in a clean bowl. For best results, use hands to knead the dough until the dough comes together)
Divide the mooncake dough into 6 equal-sized pieces and roll into a ball (about 20-30 grams of dough each)
Prepare the filling- finely mash the cooked purple sweet potato using a fork or potato masher. Do a quick taste test and lightly sweeten with sugar if desired or use without the sweetener. Roll the mashed purple sweet potato into a heaping tablespoon-sized balls (about 30g). Set aside.
Flatten the mooncake dough into a thin disk using the palms of your hands, place about 30g of filling in the middle.
Cover the sweet potato filling with the dough and gently squeeze the mooncake dough into a ball**
Use a well-greased mooncake mold to press the dough into shape. A non-stick cooking spray works well to ensure that the mold is properly greased.
Bake in a 350F pre-heated oven for about 10-12 minutes, or until the tops of the mooncakes appear dry. The bottom of the cakes should be lightly browned.
For best flavor and texture, let the mooncakes cool in the fridge overnight (or at least 8 hours) sealed inside an airtight container. This extra step ensures that the mooncake crust to soften and become more chewy, rather than tough.