Line 2 baking sheets with parchment paper and set aside. Then preheat your oven to 350ºF.
Add the finely chopped dark chocolate into a microwave-safe bowl. Then heat the chocolate 20 seconds at a time stirring in between. Once the chocolate is fully melted, set it aside for later.
In a separate bowl whip the egg whites using an electric hand mixer on high speed. This should take about 1 minute.
Then add powdered sugar and mix it in for another minute.
Next, add the cocoa powder, salt, and vanilla extract. Mix everything thoroughly.
Now use a spatula to fold in the melted chocolate and finely chopped pecans. Note: The cookie batter/dough will look runny at first, but it will thicken up quite fast.
Scoop out mounds of the cookie batter using a medium-sized scoop and place them 2 inches apart on your prepared baking sheet and bake for about 10 minutes. Once they’re baked, lightly tap the baking sheet on the counter to slightly flatten the cookies. Note: let them cool completely on the parchment paper before lifting, or else they may stick to it and tear.
Notes
Slowly melt the chocolate- Make sure you stir every 20 seconds to make sure you just melt it and don't overheat it. This can cause it to scorch and be ruined.
Whip the eggs- Whipping the egg whites on high speed will help them foam up and incorporate air into the cookie dough, making them lighter and fluffier.
Spread the cookie dough out- Leave about 2 inches in between the cookies because they will spread a bit and this will keep them from running into each other.
Be gentle- These cookies are very delicate, let them cool completely before removing from the parchment. Lifting them when they are still warm can cause them to tear or collapse.