Mix the butter and icing sugar together until very soft and creamy. I used a wooden spoon.
Fold in the blueberry powder, flour, cornflour and baking powder and mix gently.
Put the mix in a piping bag with a star nozzle and pipe swirls onto a lined baking tray.
Chill the tray for 15 minutes before baking.
Bake at 170 degrees (fafor 13-15 minutes until lightly golden.
Allow to cool on the tray for five minutes before moving the whirls.
Pipe blackcurrant curd on one upturned biscuit then sandwich with another biscuit.
Dust with icing sugar and serve.