In a medium bowl, sift together the flours, cocoa powder, espresso powder and baking soda. Add salt and set aside.
In a food processor fitted with the metal blade, add the sugar and chocolate chips and process until the chocolate is very fine.
Using an electric mixer or stand mixer, beat the eggs, vanilla extract and hazelnut extract until combined. Add the sugar mixture and mix until combined, about 1 minute.
Reduce speed to low and slowly add flour mixture and mix until just combined. Fold in hazelnuts.
Preheat oven to 350°F. Line baking sheet with parchment paper. Divide dough in half and place on baking sheet. Shape dough into two 11x2 inch or 8x4 inch logs, keeping at least 3 inches between them. Brush each log with egg white and sprinkle 1 teaspoon sugar over the top and sides of each.
Bake for 35 minutes or until the biscotti is firm to the touch. Remove from oven and let cool slightly for 10 minutes.
Transfer logs to cutting board and cut on the diagonal ¾" thick slices with a sharp serrated knife. (If it's crumbly, let cool for longer) Arrange the slices on the baking sheet and bake for 20-30 minutes, flipping the biscotti halfway through. Transfer to a wire rack and allow to cool.
Notes
Toast the hazelnuts as it draws the natural oils to the surface, intensifying the rich nutty essence, creating a deeper color, and making the hazelnuts crunchier.
If you don't want your biscotti to spread much, place in the fridge for an hour before baking.
Use a serrated knife (preferably a bread knife) in a sawing motion to cut nice smooth clean slices.
If you want long chocolate biscotti slices, slice at an angle. If you want shorter, just slice straight.
After first bake, allow biscotti to cool for 10 minutes before slicing. If you cut immediately, the slices will crumble and if you wait too long, the biscotti will be hard to cut.
Allow biscotti to cool completely after second bake. It will harden as it cools and get the texture you expect.