Crack open 5 salted duck eggs and separate the yolks from the whites. Clean the yolks on running water. Place the yolks on a heat-proof plate or bowl.

Spray the yolks with a small amount of Shaoxing wine/baijiu/other alcohol to remove the fishiness.

Place the yolks on the preheated steamer and steam on medium heat for 8-9 minutes or until cooked.

Transfer the mixture to a non-stick frying pan. Heat on low heat and cook until the mixture is just warm to dissolve the sugar. Do not boil.

Line a small freezer-friendly container with cling wrap. Transfer the mixture to the container. Freeze for 2-3 hours or until firm to touch.

Remove the frozen lava filling from the container. Use a knife to divide it into 15 pieces equally (9-10 gr each). Shape into balls and place them in a freezer-friendly airtight container. Make sure to work fast or the lava filling will melt.

Freeze the balls for at least 4 hours or overnight.

Blend 2 steamed salted egg yolks and other ingredients with an immersion blender or blender until smooth.

Transfer the mixture to a non-stick frying pan. Heat on low heat. Keep stirring the mixture with a spatula while cooking and cook until it thickens and turns into a dough. Don't overcook or it will turn dry and crumbly.

While the dough is still hot, cover with a cling wrap to prevent it from drying out. Once the dough has cooled completely at room temperature, store it in the refrigerator until using it.

In a medium bowl, add salted butter and sift in confectioners' sugar. Mix until well combined with a spatula or mixer.

Add egg yolk and evaporated milk. Mix until combined.

Sift in cake flour and custard powder. Mix until well incorporated.

Wrap the dough with a cling wrap and let it rest in the refrigerator for 1 hour.

Remove the custard filling from the refrigerator. Divide the custard filling into 15 pieces equally (21-22 gr each). Shape into balls.

Take a custard ball and make a deep well in the middle with your thumb. Insert one frozen lava ball into the middle and then close the top and reshape it into a ball. Repeat for the remaining 14 pieces. Make sure to work fast or the lava filling will melt. Just take out 3 lava fillings from the freezer at one time to prevent the lava fillings from melting.

Freeze the filled custard back into the freezer until you are ready to assemble the rest of the mooncakes.

Remove the skin dough from the refrigerator. Divide the dough into 15 pieces equally (18-19 gr each). Shape into balls.

Take 3 fillings out from the freezer at one time to prevent the lava filling inside from melting. Flatten a mooncake skin dough ball with your palms. Place a filling in the middle of it. Lift and stretch the dough over the filling to cover completely, and pinch to seal. Roll between your palms to smooth it out.

Place the mooncakes on a freezer-friendly airtight container or a baking sheet. If using a baking sheet, cover the mooncakes with a cling wrap to prevent freeze burn. Freeze the mooncakes for at least 4 hours or overnight.

Preheat the oven to 425F/220°C. Line a baking sheet with parchment paper or baking mat.

Place the frozen mooncakes on the prepared baking sheet. Spray with water to prevent drying out and cracking in the oven.

Bake for 5 minutes. Take the mooncakes out of the oven. Let them cool on the pan for 10 minutes.

Bake for another 8-10 minutes or until golden brown. Don't bake for too long or the mooncakes will crack.

For the best lava experience, the mooncakes must be consumed warm. You can also reheat the mooncakes in the oven or microwave to make the filling runny again.