Prepare the Purple Sweet Potatoes: Peel and slice the purple sweet potatoes into thin pieces, then steam them until fully cooked. Once steamed, mash the purple sweet potatoes into a smooth paste.

Make the Filling: Take 300g of the mashed purple sweet potato, mix in 30g of sugar and the condensed milk, stirring until evenly combined. Set aside.

Make the Dough: Mix the remaining mashed purple sweet potato with 100g of water, then gradually add the glutinous rice flour and rice flour. Knead the mixture into a dough. Since the water content in purple sweet potatoes can vary, you may need to adjust by adding more water if the dough is too dry or more flour if it’s too wet. For a smoother dough that's easier to work with, steam a small portion of the dough first, then knead it back into the original dough.

Shape the Mooncakes: Divide the dough into 30g portions and roll each into a small ball. Flatten each ball into a little nest shape. Spoon in the prepared filling, pinch the edges to seal, and roll it back into a round shape. Lightly dust with flour to prevent sticking, then press into a mooncake mold to shape.

Steam the Mooncakes: Place the shaped mooncakes into a steamer, leaving space between each one. Start with cold water, then steam for 12 minutes once the water starts to boil.