Orange Marble Cake

Bought some oranges a few weeks ago and it tasted really sour.  Can't seems to get another interested in eating it fresh.  So decided that I should use it as an ingredient instead.  So adapted a recipe from one of my earlier post and made this Orange Marble Cake.  The cake turns out really moist and the cocoa and orange combination was actually quite nice.  My only issue now is how to make the swirl such that the cake looks like a marble cake ;p

Orange Marble Cake

Ingredients & Directions

• 150g self-raising flour
• 125g salted butter
• 110g sugar
• 2 eggs (beaten)
• 2 tsp cocoa powder
• 1/2 tsp vanilla essence
• 1 tbs milk
• 1 tbs orange juice
• 1 tsp orange cest

1.  Cream butter and sugar until light and fluffy.
2. Add egg mixture gradually, beat well after each addition
3. Fold in sifted flour lightly into the mixture
4. Add orange juice, milk and vanilla essence and mix well.
5. Divide mixture into 2 equal portions
6. Add cocoa powder in one portion.
7. Scoop the white batter into a 6 inch oiled baking pan, then scoop the cocoa mixture on top. 
8. Use a teaspoon or sharp object to stir the batter lightly, but don't overmix.
9. Bake in a preheated oven at 175 deg cel for about 30 to 40 minutes or until skewer comes out clean.
10. Leave to cool & Enjoy!.