Pre- heat oven to 350° F (180°C) Grease and flour an 8 inch cake pan (20cm)
In a food processor add the flour, baking powder, salt, butter, sugar, eggs, yolk, milk and vanilla. Process for approximately 2 minutes until combined. Separate the batter evenly into 2 bowls, one bowl add the cocoa and combine well.
If you do not have a food processor then in a mixing bowl beat the butter and sugar together until creamy, add the eggs, one at a time, mixing well after each addition, beat in the milk and vanilla. Fold in the flour and combine until smooth.
Alternately spoon the vanilla and chocolate batter into the prepared cake pan, even the top with a spatula and with the tip of a knife swirl it in the batter to make a marble effect. Bake for approximately 45-50 minutes, test with a toothpick for doneness. Let cool 20 minutes in the pan then move to a wire rack to cool completely. Enjoy!
CHOCOLATE GANACHE
In a small pan heat the butter and cream until hot but not boiling, remove from the heat and add the chocolate stir until smooth, let cool to lukewarm and it has thickened, drizzle or pour over the completely cooled cake.
Notes
Homemade cake/pastry flour - For every cup of all purpose flour, remove two tablespoons and replace with two tablespoons of corn starch. Be sure to sift the flour and cornstarch together a couple of times, this way it is sure to be properly combined and lump free. Homemade self rising flour - To make your own, whisk together 1 cup of flour, 1 1/2 teaspoons baking powder and 1/4 teaspoon of salt.The cake unglazed can be kept covered at room temperature up to 2 days. The cake wrapped tightly in plastic can keep for 3-4 days in the fridge. Bring to room temperature before serving.The cake should be stored in an airtight container or a covered cake dish. It will keep at room temperature for approximately 1 day if glazed.The cake can also be frozen. Wrap the completely cooled cake tightly in plastic and foil, then place in a freezer safe bag or container. It will keep for up to three months in the freezer. I recommend freezing the cake without the glaze.Defrost in the refrigerator and then allow to rest at room temperature before adding the ganache. I do not recommend adding any ganache until just before serving for best results.