Preheat the oven to 170C/150C fan/325F/Gas 3. Line a large baking tray with baking parchment.
Mix the flours in a large bowl with the sugar, cranberries, cashew nuts, bicarbonate of soda, baking powder, cinnamon, mixed spice and salt.
Make a well in the centre and add the eggs, vanilla seeds (or extract) and mix everything together well. It will start to lump together, but then get your hands in and really squidge it all together to form a dough.
On a lightly floured surface, roll the dough out into a sausage shape about 30cm/12in long and 5cm/2in wide. Carefully lift it up and transfer it to the prepared baking tray.
Then, press it down gently so it becomes 1.5cm/ 5/8in high.
Bake for 30 minutes, or until firm and a knife pierced into the centre comes out clean. Remove from the oven and leave until cool enough to handle.
Carefully transfer from the baking tray and onto a board. Using a sharp and serrated-edge knife, cut thirty 1cm/½in thick slightly slanted slices. Some bits may crumble off a bit as you cut, but it’s okay. Just slice really slowly holding the biscotti ‘log’ with the other hand. Any bits that fall off are a nice chef’s perk!
Arrange the biscotti slices lying flat on the baking sheet and return them to the oven to bake for 40 minutes, turning them over half way through. Remove from the oven and leave to cool completely.
For me these are best served dunked into something hot.