A very light and moist sponge so really needs to be eaten within 24 hours of making. It is not a stodgy cake at all and you can really taste the orange.
Cake couldn't be easier. Combine 175g butter (or stork works just as well and doesn't need softening), 175g caster sugar, 175g self-raising flour, 3 eggs, 1.5 tsps baking powder and the grated rind and juice of one orange. You really do taste the orange so choose a nice juicy one. The thickness of the skin also makes a difference- those with a lot of pith tend to have a more bitter taste.
Once it is all combined pour into a 20cm deep round cake tin that has been greased and lined. Bake at about 170 degrees for about 40 minutes until it is golden and risen and springs back to touch.
Then combine 100g icing sugar with the juice of about half an orange until it is a coating consistency. Pour this over the cake and smooth with a palette knife. Then decorate with some grated orange (use the one that you took the juice for the topping from).