1. Preheat oven to 160˚C.

2. Line 12 cupcake cases/cups with parchment paper.

3. In a bowl, lightly beat eggs, add butter and sugar, then mix until light with the Bosch kitchen machine at speed 4 for 10 minutes.

4. Add milk and flour, stir until combined. Beat for 2 minutes, until light and creamy.

5. Divide mixture into 2 bowls.

6. Add orange juice and peels to first bowl.

7. Add cocoa powder to second bowl.

8. Add the mixture into each cupcake paper and stir gently to get a marble effect.

9. Bake for 18-20 minutes until firm to touch. Allow to cool.