Preheat oven to 350 degrees. Line a baking sheet with parchment or a silicone baking mat.

Sift together the flour, cocoa, baking soda, baking powder, and salt.

With a mixer, cream the butter and sugar on medium speed for about 2 minutes until light. Scrape down the sides of the bowl and add the eggs and vanilla; beat for another 2 minutes. Decrease the speed to low and mix in the dry ingredients in 3 additions, mixing only until a dough forms. Scrape down the sides of the bowl and mix in the chopped nuts and chocolate.

Turn the dough out onto a work surface and knead a few times just to incorporate any dry ingredients that didn’t get mixed in before. Divide into two portions; on the baking sheet, shape each portion into a 12 x 2 inch log. Sprinkle each log with a little sugar. Bake for 25 minutes.

Remove the sheet from the oven and let it cool on a rack for 20 minutes. Then, with a very sharp, serrated knife, slice the logs into about ¾ – 1 inch slices and leave the slices standing up on the baking sheet. Return to the oven for another 10 minutes of baking.

Transfer biscotti to a rack to cool.