Preheat the oven to 180°C (356°F).
In a bowl, add the eggs and sugar, and mix well.
Add milk and cooking oil, then mix together.
Sift in cocoa powder, cake flour, and baking powder, and mix until just combined.
Pour the batter into a cake pan.
Bake in the preheated oven at 180°C for 25–30 minutes.
Cool on a wire rack.