For the biscotti, preheat the oven to 150C/300F/Gas 2. Line a baking tray with greaseproof paper.
Mix together the flour, sugar and baking powder in a bowl until well combined.
Whisk in half of the beaten eggs until well combined. Gradually add the remaining beaten egg, a little at a time, making sure all of the egg has been fully incorporated into the mixture before adding more, until the mixture comes together as a dough. (NB: You may not need to use all of the egg.)
Add the cherries, hazelnuts and lemon zest and mix well.
Divide the dough into six equal portions. Roll each portion into a sausage shape about 3cm/1¼in in diameter, using your hands. Gently flatten each portion of dough with the palm of your hand.
Place each dough 'sausage' onto the prepared baking tray, leaving a 6cm/2½in gap between each portion of dough to allow for expansion. Bake in the oven for 15-20 minutes, until pale golden-brown.
Remove the 'sausages' from the oven and set aside for 10 minutes to cool and firm up.
Using a serrated knife, cut 5cm/2in thick slices from the dough 'sausages' on the diagonal. Arrange the slices onto the lined baking tray and return them to the oven for a further 6-8 minutes.
Turn the biscotti over and continue to bake for 6-8 minutes, or until crisp and golden-brown. Set aside to cool on a wire rack.