Mix all ingredients except the butter.

Add butter and mix until combined.

Pour into a large bowl and steam on low heat until the custard sets. The custard will be ready when a fork inserted in the middle comes out clean.

Remove from heat and allow to cool. Stick it in the fridge for a few minutes so it cools further.

Put the custard on a clean surface and knead it with your hands until it looks smooth and shiny.

Set aside 14 ounces of the custard. Put the rest back in the fridge.

Mix together everything except the water.

Slowly add the water, kneading as you go.

Place the dough in a bowl, cover with plastic film, and let it set for 30 minutes

Mix all ingredients.

Place the oil pastry in a bowl, cover with plastic film, and let it set for 30 minutes.

Divide the custard into 16 equal portions.

Put half an egg yolk inside each custard portion and roll it into a ball.

Divide the water pastry and the oil pastry into 8 equal portions each.

Use a rolling pin to flatten a portion of the water pastry. Wrap a portion of the oil pastry into the water pastry and roll it into a ball so that the oil pastry is now inside the water pastry.

Repeat until you have 8 balls.

Use a rolling pin to roll out each pastry ball into a flat oval shape, then roll them back up into a Swiss roll shape.

Cover the 8 rolls with plastic film and let them rest for 30 minutes.

Cut the rolls into halves to form 16 rolls.

To put the custard and egg yolk filling into the rolls, roll out each piece of dough, then place the filling inside the piece. Roll it back up into a ball. Repeat with each one.

Preheat oven to 356° Fahrenheit (180°Celsius). Put the rolls on a baking tray lined with parchment paper.

Evenly separate the mooncakes on the baking tray.

Brush each mooncake with the egg wash and sprinkle on the sesame seeds to garnish.

Bake for 25 minutes and serve immediately.