Preheat the oven to 170°C and grease two baking sheets.
Spread the hazelnuts on a baking sheet and toast in the oven for 10 minutes. Leave to cool and roughly chop a third of the nuts.
Cream together the butter and sugar. Whisk together the eggs, orange rind, baking powder and salt and add to the sugar mixture. Stir in the cocoa powder, polenta, whole and chopped nuts and 500 ml of the flour.
Turn out the dough on a floured surface and knead until smooth.
Add the remaining flour a little at a time, kneading until the dough is soft but not sticky.
It may not be necessary to use all the flour. Divide the dough into four uniform pieces and shape each piece into a fairly flat roll 5 cm wide and 2 cm high.
Put the rolls on the greased baking sheets and bake for 35 minutes or until the edges begin to brown.
Leave to cool on a rack for 10 minutes before cutting each roll into 1 cm thick diagonal slices.
Arrange slices on the baking sheets and bake for another 10 minutes or until golden brown. Leave to cool
before storing in an airtight container.
Serve the biscotti with cappuccino.