Beat the eggs and sugar well. Then mix the yogurt and soda and add them to the mixture. Add the oil. Finally add the flour and vanilla parts, stirring constantly. Grease a cake pan with sunflower oil and sprinkle with a little flour to cake can be peeled off easily after being ready. Pour half of the mixture into the cake. In the other half pour the cocoa and stir until a thick brown color. Pour the colored cocoa mixture. Bake for 30-40 minutes in a preheated oven at 180C degrees.