Preheat the oven to 180 C / Gas 4. Grease a 900g (2 lb) loaf tin and line with baking parchment.
In a mixing bowl, beat together the butter and caster sugar until fluffy. Add the eggs and beat until pale and creamy. Sift in the flour and fold, then sprinkle in the zest and mix.
Bake in the preheated oven for 25 to 30 minutes or until risen and golden and a skewer inserted into the centre comes out clean. Remove from the oven and allow to cool in the tin.
For the topping add juice into a bowl and little by little add the icing sugar, this should turn into a nice smooth glaze. With a skewer poke some holes into the cake then pour over the cake once it has cooled. Allow the glaze to set then remove from the tin, slice and serve.
You may want to serve hot with some ice cream, the topping is just a suggestion of mine it takes brilliant with out.