Preheat the oven to 200C/400F/Gas 6.
Place all the ingredients except the icing sugar into a large bowl and mix well to make a dough.
Turn the dough out onto a floured surface and roll into a sausage shape. Cut into 1cm/½in slices and place the slices onto a non-stick baking sheet.
Transfer to the oven and bake for ten minutes, turning once halfway through the cooking time, until golden-brown.
To serve, place the biscotti onto a plate and dust with icing sugar.