Preheat oven to 180 degrees C. Toast the almonds until golden brown.
Let almonds cool, then chop into 5mm pieces.
Set oven temperature to 170 degrees C.
Cream the butter and sugar until smooth and creamy. Beat in the eggs until smooth. Zest the orange, add to mixture and stir well. Add the orange-flavoured liqueur and cinnamon. Mix in the flour, baking powder and salt. Beat until just mixed. Stir in the chopped almonds. Divide the dough in half on a lightly floured board and form into long rolls, about 5cm in diameter and 20cm long.
Set the rolls on a baking tray and bake for about 25 minutes, or until they are brown on top.
Let the rolls cool for 5 minutes, then slice diagonally 1cm thick.
Lay slices back flat on baking tray and cook for another 10 minutes. Flip biscotti over and cook for another 10 minutes. Let cool on wire racks. If you keep these in an airtight container, they will keep for months.