A classic flavour combination of chocolate and orange, this cake is perfect as a self-indulgent snack.
Preheat oven to 180C and grease and line a 20cm square or round cake tin.
Cream the butter and sugar together until pale and fluffy. Add the eggs, one at a time, beating well between each addition. Fold in the flour and buttermilk.
Scoop half of the mixture into a separate bowl and fold in the cocoa powder. Fold the orange zest and food colouring into the rest of the batter.
Using an ice cream scoop, scoop the batter into the cake tin, mixing up the two flavours. Then, using a skewer or sharp-pointed knife, gently swirl them around to create a marble effect.
Bake for 25 minutes or until cooked through. Let cool on a wire rack.
Once completely cool, mix together the icing sugar, cocoa powder and orange juice until you have a lovely thick icing mixture.
Spread this over the cake and let set before slicing into thick squares and serving with a big cup of tea.