Preheat the oven to 190°C/gas mark 5. Cream the butter with the icing sugar until fluffy, then beat in the flour, baking powder and vanilla extract.
Spoon into a piping bag with a large star nozzle and pipe into 6cm fingers, spaced apart, on 2 baking trays lined with baking parchment. Chill for 30 minutes.
Bake for 12 minutes then cool completely on a wire rack. Dip the ends into the chocolate and leave to set on the baking parchment.