Mix butter, icing sugar and flour in food processor or electric mixer. Pat dough evenly into a 23cm tart tin and bake for 12 to 15 minutes, until golden.
Meanwhile, combine eggs, caster sugar, lemon rind, lemon juice and flour and mix until smooth. Pour mixture into hot pastry case and bake for 15 to 20 minutes, until filling is firm. Let cool completely in tin.
To serve, dust with icing sugar and cut into 12 slices.