Requires: Piping bag with 6B star nozzle and 2 silicone baking mats (alternatively, baking trays lined with non-stick baking paper)
Preheat the oven to 180°C conventional oven (350° Fahrenheit/Gas 4). Adjust metal racks to the middle groove of the oven. Prepare 2 silicone baking mats on a work surface (alternatively, use non-stick baking paper). Set aside 2 baking trays the same size as the silicone baking mats (or baking paper).
Using an electric mixer, beat the butter and icing sugar (confectioners’ sugar) until light and fluffy. Sift the corn flour and flour and beat into the butter mixture until just combined. Use your hands to mix in the orange zest and vanilla bean (or vanilla bean paste).
Note: 00 is a powder-fine Italian type of flour. It is made from soft wheat varieties, and is frequently used in Italian desserts and pastas. 00 flour is available in most supermarkets, Italian food stores and gourmet delicatessens.
Spoon the biscotti mixture into a disposable piping bag fitted with a 6B star nozzle. Pipe fingers, about 7.5cm long and spaced evenly apart on the silicone baking mats (or non-stick baking paper). Transfer the silicone baking mats (or baking paper) to trays and refrigerate the biscotti in baking trays for 40 minutes.
Remove biscotti from the fridge and bake, one tray at a time in the oven for 12-15 minutes. Transfer to a wire rack to cool completely.
Place the chocolate into a small heatproof bowl (or small saucepan) over a saucepan containing hot water. Stir the chocolate using a metal spoon until melted.
Dip one end of the biscotti viennesi into the melted chocolate, then place onto baking paper to set – buon appetito.
Tip: After dipping in chocolate, you could also dip the ends in finely chopped pistachios. I recommend baking the biscotti the day before dipping in chocolate. If the biscotti are too fresh, the heat of the chocolate can make the biscotti break.