Preheat the oven to 350 degrees Fahrenheit (with rack in center) and line a large baking sheet with parchment paper.
In a larget bowl, whisk together the flour, cocoa, baking soda, baking powder, and salt. Set aside.
In the bowl of a stand mixer, fitted with a paddle attachment, beat the butter and sugar together for 2-3 minutes, or until the butter is pale in color. Add the eggs, orange extract and zest and continue to beat for another minute or two–scraping down the bowl with a spatula to incorporate the ingredients.
Reduce speed to low and add the dry ingredients, in batches, until well mixed and a smooth dough has formed.
Divide dough in half, and roll each half into a 12″ log.-Place both rolls on the prepared baking sheet, with an inch or two in between for spreading, and use your hands to flatten and shape each into a 3″-4″ wide, 3/4″-1″ thick rectangle (still 12″ long)
Sprinkle the tops with a little sugar and bake for 25 minutes, or until the logs are firm to the touch. Remove from oven (but leave it on) and allow to cool on a baking sheet for 20 minutes.
Remove to a cutting board and use a serrated knife to cut each log into 3/4″ pieces (across the short side, so you’ll have 3″-4″ x 3/4″ pieces.)
Place the pieces, flat back onto the baking sheet, and bake for an additional 10 minutes. Remove to a cooling rack and cool completely before dipping into chocolate.
In a microwave safe bowl, melt the chocolate for 30 seconds, and then 15 seconds a at a time until mostly melted. Stir with a spoon until completely melted. Place chocolate in a shallow wide dish (I also melted mine in this dish to save dirtying and extra dish,etc. Mine was microwave safe – I recommend doing this if possible.)
Dip one flat side of the biscotti into the chocolate, coating about half way, and then lay on wax paper or your cooled parchment baking sheet, chocolate side up. Sprinkle with orange zest, if desired. Repeat with remaining biscotti.
Allow chocolate to cool and harden and then store in an airtight container for up to a week.