01 - Combine golden syrup, vegetable oil, and alkaline water in a mixing bowl. Whisk until the mixture is thoroughly blended and emulsified.
02 - Add flour to the wet mixture. Stir with a spatula until a cohesive dough forms. Cover tightly with plastic wrap and let rest at room temperature for 2 hours to allow the gluten to relax.
03 - Preheat oven to 350°F.
04 - Divide the lotus seed paste into 12 equal portions, approximately 1.4 oz each. If using salted egg yolks, encase each yolk within a portion of paste and roll into smooth, round balls.
05 - Divide the rested dough into 12 equal portions, approximately 0.7 oz each.
06 - Flatten each dough ball into a thin disc. Place one filling ball in the center and carefully wrap the dough around it, pinching the edges to seal completely. Ensure the filling is fully enclosed.
07 - Lightly dust the interior of a mooncake mold with flour. Place a filled ball inside, seam side up, and press the mold firmly to imprint the design. Release onto a parchment-lined baking sheet.
08 - Repeat the shaping process with the remaining dough portions and filling balls, arranging them 2 inches apart on the prepared baking sheet.
09 - Bake for 5 minutes to set the pastry structure.
10 - Remove from oven and lightly brush the tops with egg wash mixture, taking care not to let excess drip onto the sides.
11 - Return to oven and bake for 15 to 20 minutes, or until the tops are golden brown.
12 - Cool completely on the baking sheet. Transfer to an airtight container and store at room temperature for 1 to 2 days before serving to allow the pastry to soften and develop the traditional tender texture.