Closely adapted from Claire Ptak. I strongly preferred these cookies sprinkled with vanilla salt--but the rest of my family enjoyed them both ways. If you can confirm that your dark chocolate (not all are!) is dairy-free, these cookies are also dairy free.
Preheat the oven to 350 F (or 320 F convection). Place racks in the upper and lower thirds of the oven.
Line 2 baking sheets with parchment paper. Set aside.
Using a heatproof bowl (glass or metal), place the chopped chocolate in the bowl and place the bowl over a pot of simmering water (you are creating a double boiler). Do not let the chocolate bowl touch the simmering water. Stir the chocolate until melted smooth and then set aside to cool a bit while you work.
Place the pecans, salt, brown sugar and cocoa in a food processor with the blade attached. Process until finely chopped.
Add the almond flour and process again. Scrape the sides if needed.
Add the vanilla and pulse a few times.
Add the egg whites and pulse. Scrape the sides again.
Drizzle the chocolate over the top of the mixture. Pulse until the mixture clumps together and forms a ball of dough (it will happen quickly).
I found it easiest to transfer the mixture to a new bowl. I used a medium sized cookie scoop, aiming for a scant 2 tablespoon scoop, to scoop the cookies out. I got 12 to a pan but then only had 4 cookies leftover, so arrange them however works best for you with no more than 12 to a pan.
Sprinkle with coarse vanilla sea salt if desired.
Bake for 12-16 minutes, until the cookie is no longer shiny wet, has puffed a bit and is set. When you tap the cookie lightly it will be dry. If you are not using convection, rotate the sheets top to bottom and front to back halfway through the baking time.
Let cool on pan for 5 minutes before removing to a cooling rack.
I highly recommend you weigh your nuts for optimal results. Nuts are particularly tricky to measure by volume, and I am grateful to Ptak for using weight measurements on her nuts. This also means that you can process your own almond meal if needed.