Step 1

For the dough: In a medium mixing bowl, combine the golden syrup, lye water and oil and whisk to emulsify. Add the flour and salt and mix with a rubber spatula until it begins to form a stiff dough. Use your hands to massage the dough into the sides and bottom of the bowl, ensuring that all the ingredients are evenly combined, and the dough is smooth and slightly oily. Wrap in plastic and let sit at room temperature while you prepare the filling.

Step 2

For the filling: In a medium mixing bowl set over a saucepan of barely simmering water, melt the chocolate chips and nut butter together. (Alternatively, you can do this in 30 seconds increments in the microwave.) When the chocolate and nut butter mixture is smooth and combined, remove the bowl from the heat and add the powdered sugar and cocoa powder. Add a few pinches of salt and mix with a spoon or spatula until it comes together, then bring together with your hands. It will seem dry and crumbly at first but the more you work it with your hands, the more it will come together and become pliable like a stiff cookie dough. Divide the filling into 12 portions that weigh about 30 grams each. Roll into balls, arrange on a countertop and cover with plastic wrap to keep from drying out.

Step 3

Unwrap the dough and divide into 12 portions that weigh about 20 grams each. Roll into balls and set aside on the counter and cover with plastic wrap to keep from drying out.

Step 4

To assemble the mooncakes: Using your hands, take one ball of dough and flatten into a 3 1/2-inch-wide circle that is about a 1/8 inch thick. Add a ball of the filling into the center of the disc of dough. Wrap the filling with the dough, gently pinch to seal and then roll in your hands to form a perfectly round ball. Repeat with the remaining balls of dough and filling.

Step 5

Arrange an oven rack in the middle position and preheat the oven to 350 degrees F.

Step 6

Line a baking sheet with parchment paper.

Step 7

Lightly dust a filled ball of dough with flour and place in the cavity of a 50 gram mooncake mold (easily available online) and then press, flip over and press down until you feel resistance. Carefully unmold and place on the prepared baking sheet. (Alternatively, you can press each ball into a regular sized muffin pan with paper liners, then peel off and place on a baking sheet. BUT most of the fun in making these are the fun shapes and the mooncake press is easy to order and pretty cheap.)

Step 8

Bake the cakes for 10 minutes then remove from the oven and allow to cool slightly (so the egg wash does not coagulate immediately). Brush with the egg wash and put back in the oven and continue baking until evenly golden brown, begin checking at 8 minutes. (If you use honey instead of golden syrup, you will not get the same coloring, but it will come close if you bake for an additional 5 minutes or so.)

Step 9

These are nice right out of the oven when they are still warm and a little soft, but when they cool the outer shell will get hard. They will soften over the next couple of days kept in an airtight container on the counter; typically, they are served on day 2 or 3.