Preheat the oven to 180°C (350°F) and grease a baking tin.
In a bowl, mix flour, cocoa powder, and sugar.
Add eggs, melted butter, and half of the milk. Mix to form a smooth batter.
Pour the batter into the prepared baking tin.
In another bowl, mix custard powder with the remaining milk until smooth.
Gently pour the custard mixture over the cake batter.
Bake for 35–40 minutes until the cake is set and the custard layer forms.
Allow it to cool before slicing and serving.