Citrus Shortbread Sandwich Biscuits

185g butter
¾ c icing sugar
½ tsp vanilla essence
1 tsp finely grated lemon/orange/lime rind
1 ½ c flour
½ c cornflour
1 tsp baking powder
Cream butter, icing sugar, vanilla and rind. Sift in dry ingredients and mix well. Form into a log and chill. When quite firm, slice thinly. Bake @ 180C for 12 minutes. Sandwich together with icing.
Icing
2T butter
¾ c icing sugar
citrus juice to mix