1.Preheat oven to 200°C (180°C fan-forced). Grease oven trays and line with baking paper.
2.Beat butter, sugar and egg in small bowl with electric mixer until light and fluffy. In two batches, stir in sifted dry ingredients.
3.Spoon mixture into piping bag fitted with 1cm-fluted tube. Pipe 3cm rosettes about 3cm apart on trays. Bake biscuits about 10 minutes; cool on trays.
4.To, make vienna cream, beat butter and extract in small bowl with electric mixer until as white as possible; gradually beat in sifted icing sugar and milk, in two batches.
5.Sandwich biscuits with vienna cream.