Heat the oven to 350 and line a few baking sheets with parchment paper.
Melt the butter in a small sauce pan over medium until foaming. Swirl the pan while you continue to heat until you see brown flecks in the bottom and it is nicely golden. Immediately pour into a bowl.
Whisk the confectioners sugar, cocoa powder and salt in another bowl. Whisk the egg whites and egg into the slightly cooled butter along with the vanilla. Add the dry mix to the wet one along with the chocolate and gently mix until combined, breaking up any clumps of cocoa powder, but some small ones are ok.
Using a medium cookie scoop (I think mine was about 1/2 tbsp or so), scoop out balls of batter/dough (it is kind of in between), leaving 2 inches of space b/c they spread out a lot. Sprinkle with the salt. Bake for 4 minutes, rotate the sheet and bake another 3-4 minutes until they have spread out and look a bit wrinkled and the center is no longer raw.
Allow to cool fully on cookie sheet before transferring to a plate or container. Try to eat only a few!