Place the chestnuts, sugar, salt and vanilla into the bowl of a large food processor.

Blitz the mixture until it is a smooth paste, adding enough boiling water as you do so until everything comes together in a smooth paste. The mixture should be like a very thick hummus.

Scrape the mixture into a large non-stick pan.

Start cooking the paste over medium-high heat.

Use a spatula or wooden spoon to stir the paste so that the moisture can evaporate from the mixture.

As you stir, add about a tablespoon of the oil at a time.

Keep stirring until the oil is well-incorporated into the paste.

Once the mixture has emulsified, add some more oil.

Continue until all of the oil has been added.

Once all of the oil has been added, continue stirring the mixture so that it can thicken.

Eventually, the goal is to be able to fold the paste from the outer-edges into the centre until the paste is a little firm and can hold its shape. By this stage, the paste will resemble a very soft cookie dough.

Be careful to not over-cook the paste as it can burn.

Transfer the paste to a large bowl and let it cool completely. The paste will firm up more as it cools.

Mix the chocolate chips through the cooled chestnut paste.

If you are making this paste ahead of time, you can keep it in an air-tight container in the fridge for several days.

Make the Mooncake Dough on the day you plan to make the mooncakes.

In a large mixing bowl, whisk together the golden syrup, oil and lye water.

Add the flour.

Mix everything together until a dough forms.

Lightly knead the dough until you have a soft and smooth ball of dough. If the dough is too crumbly and doesn't come together well, add some water.

Wrap the dough in some plastic wrap.

Leave the dough to rest at room temperature for at least 30 minutes.

For a 50 g mooncake mould, the filling should weigh 30 g (together with the Mooncake Dough of 20 g, the cake will weigh 50 g).

For a 100 g mooncake mould, the filling should weigh 60 g (together with the Mooncake Dough of 40 g, the cake will weigh 100 g).

Portion the Chestnut Paste as necessary using a digital kitchen scale. This recipes makes about 20 x 50 g mooncakes, so measure out 20 portions of the Chestnut Paste.

Roll each piece of Chestnut Paste into a ball.

Place the balls of Chestnut Paste in the fridge while you get on with the rest of the recipe.

For a 50 g mooncake mould, the Mooncake Dough should weigh 20 g.

For a 100 g mooncake mould, the Mooncake Dough should weigh 40 g.

At this stage, the dough should feel slightly oily and sticky.

Portion the dough as necessary using a digital kitchen scale. You should have enough dough for about 20 mooncakes.

Roll each piece of dough into a smooth ball.

Line a large baking tray with baking paper.

Flatten a piece of Mooncake Dough into a thin round shape which is just large enough to encase the filling.

Bring the edges of the dough up around the filling, cupping the mixture between your thumb and forefinger as you do so.

Gently pinch the dough until it stretches to completely cover the filling.

Pinch any cracks together, or even add a bit of extra dough to patch up any cracks if necessary.

Roll the mixture into a smooth ball.

Place the balls of filled dough onto the lined baking tray.

Prepare the mooncake moulds by affixing your desired stamp to the plunger.

It may be wise to lightly dust the moulds with some flour to stop the cakes from sticking to the stamps. But I generally find that the dough does not stick, especially if you are using the plastic mooncake moulds like I have.

Place one ball into the mould. For square moulds, I recommend gently pushing the ball of dough into a squarish-shape with your fingers before inserting it into the mould.

Place the plunger directly onto the baking tray, and press the plunger down with some gentle pressure. If you press down too hard, you might flatten the cakes too much.

Gently release the mould from the cake.

Repeat with the remaining balls of filled dough.

The cakes do not spread as they bake, but I would still recommend spacing them apart so that they bake evenly.

Preheat the oven to 180°C/356°F (without fan).

Bake the mooncakes for 10 minutes.

Remove the baking tray from the oven and let the cakes cool for 10 minutes.

Reduce the oven temperature to 160°F/320°F (without fan).

Meanwhile, make the Egg Wash by whisking the egg with some water in a small bowl.

Lightly brush the mooncakes with the Egg Wash, using a pastry brush with fine bristles (a silicon brush picks up too much egg wash for this task). Try to avoid putting too much Egg Wash onto the intricate patterns on the surface. If you have too much Egg Wash on the cakes, use some kitchen paper to blot the cakes.

Return the baking tray to the oven.

Continue baking the mooncakes for 10-15 minutes, or until they are golden brown all over.

Let the mooncakes cool completely on the baking tray, which will allow them to develop a crisp bottom.

Store the mooncakes in an air-tight container at room temperature for up to 1 week.

The mooncakes are typically served after 1-2 days when the dough has softened slightly and the patterns become more settled and defined. However, I recommend trying at least one while it is still fresh and the dough is somewhat crispy.

The mooncakes can also be stored in an air-tight container in the fridge. Bring the cakes to room temperature before serving.