Preheat the oven to 190C/375F/gas mark 5
Use a 20cm/8 inch round cake tin.
Grease the cake tin and dust with flour. Beat together the butter, lemon rind and sugar until pale and creamy. Stir in the sour cream and milk then fold in the sifted flour, cornflour and baking powder. Turn into the prepared cake tin, smooth over the surface, and bake for 40-50 minutes. Turn on to a wire rack to cool.
Syrup and icing: Bring the water to the boil with the lemon juice and sugar. Add the concentrated apple juice and pour slowly over the cake, allowing the syrup to soak well in.
Mix the sifted icing sugar with the lemon juice until smooth and spread thickly on top of the cake, allowing it to fall over the sides. Shred the strip of lemon peel and sprinkle over the icing before it sets.
