FOR LEMON FILLING = put cornflour, caster sugar, lemon rind into a saucepan. pour in a little water and blend to a smooth paste. Gradually add the remaining water and lemon juice. Bring to the boil on medium heat stirring constantly. Reduce heat and simmer gently for 1 min until smooth and glossy. remove from heat and beat in the egg yolks one at the time, then beat in butter .put saucepan in a bowl of cold water to cool filling, when cool,soon mixture into the pastry case that had been prepared earlier.