Preheat the oven to 170 degrees C (340 degrees F).
Grease an 8 inch round cake pan with Butter (to taste), line base with parchment paper. Sift Cake Flour (220 gram) and Baking Powder (1/2 tablespoon) together, set aside.
Beat Salted Butter (250 gram) and Caster Sugar (160 gram) until pale and fluffy at medium speed for about 5 minutes. Reduce speed, add Vanilla Extract (2 teaspoon). Add Large Egg (4) one at a time beating thoroughly after each addition.
Add in half of the flour followed by the Natural Unflavored Yogurt (200 gram) and remaining flour, beating until just incorporated.
Take out half of the plain batter and blend well with the Unsweetened Cocoa Powder (1 1/2 tablespoon) mixed with Milk (2 tablespoon).
Spoon 3 headedl tablespoons of the plain batter into the middle of the cake pan. Straight away spoon 2 headed 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 drawing the skewer up the opposite way.
Bake in the preheated oven for about 45-50 minutes or until a skewer put into the center of the cake comes out clean.
Leave the cake to cool in the pan for 10 minutes, then put the cake onto the rack to cool completely. Serve and enjoy!