Weigh/measure out your butter, caster sugar and flour into a bowl.
110 g butter, 110 g caster sugar (superfine sugar), 110 g self-raising flour
Crack in the eggs and mix until smooth.
2 eggs
Split the mixture in half.
Keep one half plain and add the cocoa powder to the other half.
2 tbsp cocoa powder
Grease a friand tray (I used a silicone one) and spoon in the plain batter.
Spoon the chocolate batter in on one side of the plain.
Use a skewer or knife to make a marble effect on top.
Bake for approximately 15 minutes at 180℃ / 350℉ or until golden brown and the cakes spring back when pressed.
Allow to cool on a cooling rack for a few minutes, then remove from the friand tray and leave to cool completely.