Marmorkuchen (German marble cake)

Method
Prep:25min  ›  Cook:1hr  ›  Ready in:1hr25min 

1. In a large bowl, beat the butter with an electric mixer until light and creamy. Add the sugar and vanilla while beating, then the eggs one at a time. Beat for 5 minutes until fluffy. In a separate bowl sift the flour with the baking powder; add it to the cake mixture, alternating with the milk. Add the rum and the lemon zest if desired.
2. Preheat the oven to 180 C / Gas 4. Butter a large Kugelhopf mould or Bundt cake tin and pour 2/3 of the cake mixture into the mould.
3. Add the cocoa to the remaining mixture, adding 2 to 3 tablespoons depending on how dark you prefer the mixture to be. Stir well until the cocoa is fully incorporated. Pour the cocoa mixture over the light mixture in the mould. Gently move a fork up and down through the cake mixture in circular movements to create a marble pattern.
4. Bake in the preheated oven for 1 hour, or until a cake tester comes out clean.
5. Let cool slightly, then unmould onto a cake rack and cool completely.

To serve...

Dust with icing sugar or glaze with chocolate icing if desired.