In a bowl add egg, sugar and vanilla and beat for 5 minutes on very high speed until the egg becomes light and fluffy.
Add oil and mix.
Through a sifter add flour, cocoa powder and baking powder. GEntly fold with a spatula.
pour milk and mix gently.
Grease a frying pan with butter and pour the cake batter into it. Reduce heat to lowest and cover the pan with a lid.
Cook for about 10 minutes until a toothpick inserted comes out clean.
TAke a baking paper and place cake on it. Roll the cake along wiht the paper and let the cake cool.