Put all the ingredients together in a large bowl and mix together lightly to form soft dough, being careful not to over-mix as the mixture will become tough. Divide the pastry into 3 pieces, and roll out each piece into a long sausage. Place them on a lined baking tray and bake for 20 minutes at 180`c. You will only be half-cooking the pastry at this stage. Remove the baking tray from the oven and leave the pastry to cool down completely for 20 minutes. Next, using a sharp knife, slice the pastry diagonally into 1cm pieces, and place them side by side on a lined baking tray. You will need to bake the biscotti in the oven again for another 10-15 minutes. This process will be drying out the biscotti on the surface to make them crunchy. Take the biscotti out of the oven and turn them around onto their opposite side. Put back into the oven and continue to cook for another 10-15 minutes. When the biscotti have been cooked on both sides, remove them from the oven and leave them to cool on the baking tray. Serve the chocolate and mandarin biscotti with a glass of limoncello or amaretto liqueur.