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.
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, so let them cool for a bit and carefully remove them from the baking sheet with a spatula.