Preheat oven at 175°C.

Oil and dust your baking tin and set aside.

Sift your flour and set aside.

In a bowl cream your margarine and sugar until pale.

Add eggs one at a time and whisk.

Add the zest and juice in the mix.

Fold in the flour and beat while adding the milk.

In another bowl, half the butter and add the cocoa powder. Mix until fully combined.

In your baking tin alternate the 2 types of batters while pouring. Using a skewer or knife whisk gently or design as you wish.

Bake at 175°C for 50mins or until skewer inserted comes out clean.

Let it cool for 10mins then remove from the tin and cool completely.