Beat together the butter and sugar together until pale and fluffy, then beat in the eggs one at a time.
Add the orange zest, juice, nuts and cranberries and beat until well combined.
Sift together the flour, cornmeal and baking powder into the bowl and beat in. Use your hands to finish bringing the mixture together to form a soft dough.
Divide the mixture into four pieces and roll each piece into a log shape about 30cm long. Place on baking sheets and flatten slightly.
Bake for 30 minutes until risen and golden, swapping the baking sheets around in the oven halfway through the cooking time.
Remove from the oven and allow to cool slightly. Reduce the oven temperature to 170°C/160°C Fan/gas mark 3.
When the logs are cool enough to handle, cut the pieces diagonally into 1cm thick slices. Place cut side down on the baking sheets and return to the oven for 10 minutes until crisp and golden. Allow to cool.
Biscotti will keep for about 4 weeks if stored in an airtight container.