01 - Preheat oven to 350°F. Line a baking tray with parchment paper and set aside.
02 - Combine golden syrup, vegetable oil, and alkaline water in a mixing bowl. Stir thoroughly until the mixture achieves a smooth, uniform consistency.
03 - Add flour to the wet mixture and blend until a soft, pliable dough forms. Cover the bowl and let the dough rest for 30 minutes at room temperature.
04 - Divide lotus seed paste into 12 equal portions, approximately 1.4 oz each. If using salted egg yolks, press one yolk into the center of each paste portion and shape into smooth balls.
05 - Divide the rested dough into 12 equal pieces, approximately 0.9 oz each.
06 - Flatten one dough portion into a thin disc. Place a filling ball in the center and carefully wrap the dough around it, sealing completely to encase the filling. Repeat with remaining portions.
07 - Lightly dust each filled ball with flour. Place into a floured mooncake mold and press firmly to imprint the pattern. Invert the mold and gently release onto the prepared baking tray.
08 - Bake mooncakes for 5 minutes. Remove from oven and allow to cool for 10 minutes on the tray.
09 - Whisk egg yolk with water until combined. Brush a thin, even layer over the surface of each partially baked mooncake.
10 - Return mooncakes to the oven and bake for an additional 15 to 20 minutes, or until the tops develop a rich golden-brown color.
11 - Cool completely on a wire rack. Store in an airtight container for 1 to 2 days before serving to allow the pastry skin to soften and develop the traditional texture.