Preheat the oven to 200°C. Place baking paper on 1 large baking tray or 2 smaller ones
In a electric mixer, mix the butter, sugar, vanilla extract and salt until light and fluffy.
Mix the flour and baking powder together and gradually add it to the mixture alternating between the milk and egg.
Add the chopped hazelnuts and mix through and then add the chopped chocolate.
On a lightly floured surface, turn the dough out. If needed work through the hazelnuts and chocolate a bit more.
Divide the dough into 4 / 8 equal sizes. Shape the dough into long sausages, place on a baking tray and flatten the top a bit with your hand.
Place in the oven and bake for 20 minutes.
Remove from the oven and turn the oven down to 100°C, allow the biscotti to cool for 15 minutes and then cut with a serrated knife to about 3cm in size.
Place back in the oven and cook for 1 - 2 hours. Remove and allow to cool.