Grease and line the bottom of 1 large loaf pans or 2 small loaf pans.
Place the superfine sugar, butter and zest of the lemon and orange in a bowl and beat together until pale and creamy.
Add the milk, and then beat in the eggs, one at a time, with a spoon of flour to prevent the mixture from curdling.
Mix in the remaining flour.
Spoon into the prepared tin/tins and level the surface flat.
Bake in the oven for about 45 minutes for a large loaf or 30 minutes for the smaller loaves until they are golden and a skewer comes out clean when inserted into the center of the cake.
While the cake is cooking, place the lemon and orange juice in a saucepan, bring to the boil and allow to reduce in quantity to about 3 tablespoons. Leave to cool, and then stir in the granulated sugar so it just starts to dissolve.
As soon as the cake comes out of the oven, prick several times with a skewer, then slowly pour the lemon and orange sugar all over the top, letting it soak into the cake. Leave to cool completely in the tin before turning out and cutting into slices to serve.