Preheat your oven to 350°F and line a large baking sheet with parchment paper.

In a large bowl, whisk together flour, baking powder, baking soda and salt. Sift in cocoa powder and whisk to blend evenly.

In a medium bowl, whisk eggs to blend evenly. Gradually stream in sugar while whisking constantly until smooth and lightened by a shade. Whisk in vanilla extract and melted butter.

Make a well in the center of the dry ingredients in the large bowl and pour in the egg mixture. Stir gently with a spatula or wooden spoon until most of the flour is absorbed. Fold in chocolate chips and hazelnuts. The dough will be stiff and a bit sticky but not wet. Use your hands to incorporate the nuts and bring the dough together if necessary.

Divide dough in half and roll each half into a 10-inch log. Flatten it down to about 2 inches wide and place onto prepared baking tray. Bake for about 25 minutes until puffed, shiny and slightly cracked at the surface.

Transfer baking sheet to a wire rack and let biscotti log cool on the pan for at least 30 minutes, or until cool enough to handle. Reduce oven temperature to 300°F.

Transfer the log to a cutting board and use a serrated knife to slice them diagonally on a sharp angle at about ¾-inch increments with a gentle sawing motion. Place cookies back onto the baking sheet so that they are sitting right-side-up and bake for 10-15 minutes until dry and crisp. Let cookies cool completely.

Melt dark chocolate gently in the microwave (20 second bursts and frequent stirring) or over a double boiler until smooth and glossy and then dip each cookie into melted chocolate. Place onto a parchment lined baking sheet to set before storing.