Simple to bake and long lasting, biscotti make perfect edible gifts. These are flavoured with lemon zest and studded with pistachios, but you could substitute these for orange and hazelnut instead if you prefer.
Heat the oven to 180°C/160°C fan/350°F/Gas 4.
Make the dough. Tip the caster sugar into a bowl and add the lemon zest. Massage the zest into the sugar until the oil from the zest is distributed evenly in the sugar. It should look very pale yellow and feel a tiny bit damp. Add the flour and baking powder and mix together with a wooden spoon.
Add the oil, egg and pistachio extract all at once and mix until just combined (don’t overmix). Add the pistachios and mix for 5 seconds until evenly distributed.
Bring the dough together and shape it into a sausage measuring about 33cm long. Place the dough sausage on the lined baking tray. Bake the dough for 20 minutes, then remove it from the oven and leave it to cool slightly. Then, cut the partly cooked dough sausage on the bias into slices about 1.5cm thick. Lay the slices on their sides on the lined tray. Reduce the oven to 170°C/150°C fan/325°F/Gas 3 and bake the slices for 5 minutes, then turn them over and bake for a further 5 minutes, until pale golden. Remove the biscotti from the oven and leave to cool and crisp up on the tray.
To decorate, melt the white chocolate in a heatproof bowl set over a pan of gently simmering water, stirring until smooth. Remove the bowl from the heat and divide the melted chocolate into 2 small bowls. Colour one bowl of chocolate green and the other bowl yellow. Pour each colour into a heat-resistant small piping bag fitted with a small plain piping nozzle.
Quickly and confidently pipe the green chocolate in fine lines over each biscotti, then pipe the yellow lines in the same way. Leave the chocolate to set before serving.