Preheat oven to 170 deg C. Grease a 8 inch round cake pan with butter or cooking spray, line base with parchment paper. Sift plain flour and baking together, set aside.

Beat butter and sugar until pale and fluffy at medium speed for about 5 minutes. Reduce speed, add vanilla extract. Add eggs, one at a time beating thoroughly after each addition.

Add in half of the flour followed by the yoghurt and remaining flour, beating until just incorporated.

Take out half of the plain batter and blend well with the cocoa paste.

Spoon 3 heapful tablespoons of the plain batter into the middle of the cake pan. Straight away spoon 2 heapful tablespoons of the chocolate batter on top. Continue doing this until all the mixture has been used. Then slightly tap and shake the cake pan to even the batter.

Create feather patterns by inserting a skewer into the batter in one direction and draw the skewer up the opposite way.

Bake in the preheated oven for about 45-50 minutes or a skewer into the center of the cake comes out clean.

Leave cake to cool in pan for 10 minutes, then turn out cake onto rack to cool completely.