Fill a double boiler with water, and bring water to a boil while you prepare custard mixture.
Cream butter and sugar until light and doubled.
Add egg and mix until well incorporated. The mixture will look like it is splitting but don’t worry, it will be fine after adding in the dry ingredients.
Add in milk powder and wheat/corn starch, then mix to combine.
Transfer mixture to a stainless steel bowl, and place onto double-boiler. Reduce to medium heat, and start whisking until mixture is smooth.
Cook on top of double boiler, stirring constantly with spatula until mixture no longer sticks to the back of the spatula. When the custard filling is cooked – it is solid and firmer in texture. Remove from stove.
Cover with layer of cling wrap and chill custard in fridge to set.
Remove custard from fridge and divide into 8 x 15g portions. Shape into round balls. Cover with cling wrap and let rest in fridge whilst you prepare your jelly.
To Make Gula Melaka Jelly
Chop gula melaka and place with water in a pan and bring to boil. Sieve to remove impurities.
Add agar-agar powder and jelly powder then stir to dissolve. Add pandan leaves and bring a simmer for 3-4 minutes. Remove pandan leaves.
Stir a pinch of salt into coconut milk, and add into jelly mixture. Stir constantly and bring up to a boil, then remove from heat immediately.
To Assemble Filling
Pour a thin layer of gula melaka jelly mixture into a smaller round jelly mould (diameter = 4cm).
Place custard “egg yolk” in the center.
Fill the mould with gula melaka jelly filling and refrigerate for approximately 20 minutes or until fully set.
To Make Coconut Milk Jelly
Combine coconut milk, water, sugar, agar-agar powder, jelly powder into a pot and mix well. Place knotted pandan leaves and stir constantly until agar-agar powder has fully dissolved. Bring to a boil then immediately turn off the heat.
To Assemble
If using fresh cendol in packet, drain cendol then place in a small bowl and cut/chop into smaller pieces.
Pour ½ cm layer of coconut milk jelly into plastic mooncake mould (diameter = 7.5cm) then spoon in some cendol pieces. Leave to cool until almost set.
Unmould gula melaka jelly filling onto a plate.
Place gula melaka filling into the centre of the mould. Pour in more coconut jelly mixture until mould is filled.
Using a small spoon, carefully spoon in cendol pieces on the sides. Allow to cool completely for approximately 15 minutes, before chilling the jelly mooncakes in the fridge.
To Serve
When fully set, unmould the jelly mooncakes. You could run a skewer through the sides of the mould or give both sides of the mould a slight squeeze to release. If not serving immediately, store jelly mooncakes in a container and keep chilled.