In a big bowl or in the bowl of your standing mixer fitted with a paddle, beat the butter and icing sugar until they are creamed, roughly 10 minutes or so.

Add one egg yolk at a time, combining well between additions, then sift in the flour and potato starch and combine.

Preheat the oven to 200C and prepare a baking dish covered with parchment paper.

Move the cookie dough into a piping bag fitted with a large star nozzle and pipe the cookies out, roughly 3cm in length. 

Bake for 12 minutes and leave to cool completely on a cooling rack.

Once cool, melt the dark chocolate and dip half of each frollini in, then place again over the cooling rack covered with parchment paper.

Wait for the chocolate to set completely before serving.