How to make
Beat the butter or margarine with a mixer for about 30 seconds. Add the sugar, baking powder and salt. Beat well. Add the eggs, yolk, milk and beat, until a smooth mixture is obtained.
Mix the flour with the mixer, as much as the mixture can absorb and add the rest with a wooden spoon. Add the crushed chocolate and walnuts.
Divide the dough in two.
Shape each half into about 5.5″ (14 cm) long roll. Place the rolls about 3″ (7-8 cm) apart on a lightly greased baking tray.
Flatten them, until they are about 2″ (5 cm) thick.
Beat the egg white with 1 teaspoon of water. Grease the shaped rolls. Sprinkle them with the extra sugar.
Bake the biscotti for 25 minutes at 390°F (200°C) or until the pastry has hardened (check with a toothpick).
Leave them to cool in the tray for about 1 hour, transfer them onto a cutting board and cut diagonally into about 1.2″ (3 cm) thick slices. Arrange the slices flat in the tray and bake for 10 minutes at 300°F (150°C).
Turn them over and bake for another 10-15 minutes or until they become dry and crunchy. Leave the biscotti to cool completely on a wire rack.
The Triple Chocolate Biscotti are ready.