Step 1: Prepare the filling by cooking the pineapple pulp, sugar, and maltose in a non-stick pan over medium heat until it becomes a thick, golden, and translucent paste. This can take 30-40 minutes. Let it cool completely and divide into 30g balls.
Step 2: In a large bowl, whisk together the golden syrup, vegetable oil, lye water, and salt until well combined.
Step 3: Sift the flour into the liquid mixture and fold gently with a spatula until a soft dough forms. Do not overmix. Wrap in plastic and let rest for 2 hours.
Step 4: Divide the rested dough into 20g portions. Flatten a piece of dough and place a pineapple filling ball in the center. Gently wrap the dough around the filling until sealed.
Step 5: Dust the mooncake mold with cornstarch, insert the ball, and press firmly onto a lined baking sheet. Repeat for all mooncakes.
Step 6: Bake in a preheated oven at 175°C (350°F) for 5 minutes. Remove, let cool for 5 minutes, then lightly brush with the egg wash.
Step 7: Return to the oven and bake for another 10-15 minutes or until the mooncakes are golden brown. Let cool completely before storing.