Preheat oven to 190oc. Arrange cake cases in fairy cake tin. Beat together butter and vanilla sugar then one by one beat in the eggs.
Into the bowl sift flour and cornflour then fold into the batter until ingredients are well combined. Stir in lemon zest. Half fill each cake case with the batter.
Bake for 15 min until risen and golden. Allow to cool on a wire rack.
Beat together icing sugar, lemon juice and boiling water until you have a smooth icing. Using a teaspoon drizzle the icing over the cakes then leave to set.