Step 1

The first step is to cream the butter with the egg yolks and icing sugar until creamy, light and fluffy.

Step 2

Add in the flour, lemon zest, Vanilla Extract and milk. Whisk until well combined.

Step 3

Combine the flour and baking soda and give it a whisk to combine. How whisk in to the wet ingredients a few tablespoons a time until combined and creamy. Don't over mix. Fold in the Chocolate Chips

Step 4

In a clean mixing bowl, whip the egg whites until stiff peaks form. Now carefully blend them in to the batter using a rubber spatula.

Step 5

For the chocolate marble, separate a little less than 1/2 the batter in a separate bowl. Sift in the cocoa powder and fold with a rubber spatula until no dry powder is left.

Step 6

Butter the Gugelhupf Pan and dust with flour, pour out any excess flour.

Step 7

Layer the cake mold with 1/2 of the white batter. Even out with the back of a tablespoon. Now add all the cocoa batter and top with the remaining white batter. Using a wooden skewer or the back of a spoon, run through the batter in a wavey form to create the marble effect.

Step 8

Bake in a preheated oven at 175 C or 345 F for 45 to 55 Minutes. To see if the cake is done, insert a wooden skewer in to the center cake. If it comes out clean the cake is ready.