Prepare the Fillings: If using salted duck egg yolks, gently rinse them and soak in a little rice wine for 15 minutes, then bake at 150°C (300°F) for 5-7 minutes until slightly firm. Let cool.

Wrap the Yolks: Divide the lotus seed paste (or other filling) into portions. Flatten each portion, place a prepared egg yolk in the center, and carefully wrap the paste around it, ensuring the yolk is fully enclosed. Roll into a smooth ball.

Prepare the Dough: In a large bowl, combine the golden syrup, peanut oil, and lye water. Mix well. Add the sifted cake flour and mix until just combined, forming a soft dough. Do not overmix. Cover the dough and let it rest at room temperature for at least 1 hour (preferably 2-3 hours).

Shape the Mooncakes: Divide the rested dough into smaller portions. Take one portion of dough, flatten it, and place a prepared filling ball in the center. Carefully wrap the dough around the filling, ensuring it's completely sealed. Gently press the ball into a mooncake mold, pressing firmly to get a clear design. Tap the mold to release the mooncake onto a parchment-lined baking sheet.

Bake the Mooncakes: Preheat your oven to 180°C (350°F). Bake the mooncakes for 10 minutes. Remove from oven and let cool for 5 minutes. Brush them lightly with the egg wash (1 egg yolk beaten with 1 tbsp water). Return to the oven and bake for another 10-15 minutes, or until the crust is golden brown. Let cool completely on a wire rack.

Cool and Serve: Allow the mooncakes to cool completely, then store them in an airtight container for 1-2 days to allow the crust to soften and the flavors to deepen. Slice into wedges and serve.