Almonds are the most traditional addition to biscotti but most nuts work well, especially hazelnuts, pistachios and macadamia nuts. Nut allergy sufferers could try pumpkin seeds or desiccated coconut.
Fruit also works well in biscotti; try grating lemon or orange zest into the dough or folding through candied peel. Cranberries and raisins or dried fruit such as figs and apricots are a welcome addition.
Try adding spices such as star anise and cinnamon or, for an English twist, add lavender.
For something a little more special, add a good glug of amaretto to the dough and dip the finished biscuits in melted chocolate.