In a bowl, mix 2.5 cups water, 1/2 cup cocoa powder, 2.5 cups full cream milk, 1 tablespoon cornstarch, 1/2 cup sugar, and 1/2 cup condensed milk.
Add 10g agar-agar to the mixture and stir until well combined.
Boil the mixture until it thickens nicely; if it’s not dark enough, you can add more cocoa powder.
Strain the mixture into a mold with a lid. Arrange Marie biscuits at the bottom of the mold.
Pour some of the mixture over the biscuits to make sure they are submerged but not completely covered.
Repeat this process by placing 3 more biscuits on top and pouring in additional mixture until you reach the top of the mold.
Cover the mold with a lid and let it set for about 30 minutes in the refrigerator.
Once cooled, unmold and serve. This puding batik can be cut into layers to show both chocolate pudding and layered biscuits.