Prep: Preheat oven to 375°F. Line a baking sheet with parchment paper. Set aside.
Determine mold size: Figure out the capacity of your mooncake mold. If you don't know what it is, wrap the mold in plastic wrap to prevent leaks and fill the mold with water. Pour the water into a cup that has been tared on a scale.
Determine ratio: From there, you can decide on the ratio of dough to filling that you want to use. For baked mooncakes, I would recommend a ratio of 1:2 or 2:3 if you want a bit more dough. For a 75g mold, a 1:2 ratio would be 25g dough and 50g filling. A 2:3 ratio (what I used for mine) would be 30g dough and 45g filling.
Portion out dough and filling: Weigh out the dough into 30g portions. Roll them in your hands to form balls. Weigh out the pineapple filling into 45g portions. Squeeze and roll them in your hands to form balls. If using salted egg yolks, weigh the egg yolks first and then add pineapple filling to make the total weight 45g. Pack the pineapple filling around the egg yolk. Place all the balls on a piece of parchment paper.
Flatten dough: Dust your hands with a bit of flour to prevent sticking. Press a ball of dough between your hands to flatten it. Place the dough on the flat palm of one hand and press it out with your other fingers until it's quite thin, about 1/16".
Wrap filling: Place a ball of pineapple filling in the middle and wrap it with the dough. Push the filling down, if needed, and push the dough towards the opening to close. Re-form into a ball. Use a bit of excess dough to patch any holes or tears. Place the ball with the seal side down on your baking sheet. Repeat with the rest of the dough and filling.
Stamp design: Insert your desired stamping plate into your mooncake mold plunger. Lightly dust each mooncake ball and the plunger with flour, tapping any excess out. Carefully lower the plunger onto a ball of dough and firmly press the plunger down 5-10 times for a clear design. Repeat with the rest of the mooncakes.
Bake: Bake mooncakes for 10 minutes. Remove them from the oven and let the tray cool on a wire rack for 15 minutes for the design to set before applying egg wash.
Egg wash: Meanwhile, whisk an egg yolk with water for the egg wash. Use a pastry brush to very gently brush a very thin layer of egg wash across the top of each mooncake.
Bake again: Return the tray to the oven to bake for another 10 minutes.
Let mooncakes rest: Let the mooncakes cool completely at room temperature. They will be hard and crumbly when freshly baked. Transfer them to an airtight container and store them in the fridge for at least 24 hours. They will soften and gain an oily sheen like proper mooncakes. Let them come back to room temperature before serving.