6oz butter or marg
6oz caster sugar
8 oz self-raising flour
8oz chocolate chips (milk or dark)
orange oil (optional)
Line and grease a reasonably deep 7 or 8 inch cake tin. Cream the butter and sugar, add the eggs, fold in the flour and choc chips. Zest the orange (quickest way to do this is with a potato peeler) and add the zest to the cake mixture. Then halve the orange and squeeze one half of the orange juice into the cake mixture. For added orangeyness (recommended), add a few drops of orange oil.
Spoon into the tin and bake for 1 hour 15 mins on about 180C (a bit less in a fan oven).
When the cake is cool, mix a few spoonfuls of cocoa powder, several spoons of icing sugar, and the remaining juice from the orange, to make choc-orange icing. Spread over the cake, and leave to set.