Preheat the oven to 170°C.
Sift the flour together with the baking powder.
Separate the eggs.
Whip the egg whites in a large mixing bowl until you get stiff peaks.
Mix the egg yolks with the sugar then continuously pour in the milk and oil, whilst stirring.
Add the flour to this mixture spoonful by spoonful then gently fold in the whipped egg white.
Transfer about half of the batter into another bowl. Add the cocoa powder to one bowl, the vanilla extract to the other. Mix well.
Grease and flour a bundt cake tin and spoon in the two batters alternating ( you can use a wooden skewer to make swirls if you like).
Bake in the preheated for 45-55 minutes until golden.