Line a baking sheet with parchment paper. If you want to use guide lines to measure your biscuits more precisely, use a ruler to draw lines on the underside of the paper, so they show through as you are piping.
Cream the butter and sugar until light and fluffy. Add the vanilla and mix to incorporate.
Stir in the sieved flour and cornflour, then add the milk, as needed, to make a soft dough.
Transfer the dough to a piping bag fitted with a large, star-shaped nozzle.
Pipe onto the baking sheet in lines about 3 inches/7.5cm long.
Place the baking sheet in the fridge for about 30 minutes to let the dough firm up.
Meanwhile, preheat your oven to 375F/190C.
Take the biscuits out of the fridge and bake for 12-15 minutes.
Remove to a wire rack to cool. When cool, dip the ends in melted chocolate and place on baking parchment to set.