Preheat oven to 350º. Butter an 8×8 or 9×9 baking pan. Parchment paper placed inside will help the brownie cookie to not stick.
In a medium bowl combine the unsweetened cocoa powder, the all-purpose flour, salt, and baking soda. Set this aside.
In a microwave safe bowl, melt the butter. Add half of the chocolate chips and the vanilla; stir until chocolate has melted and combined with the butter. Set aside.
In a mixing bowl, combine the eggs and brown sugar substitute. Add the melted chocolate and butter; combine stirring gently. Add the flour mixture and chopped nuts, a little at a time, stirring until well combined. Stir in the remaining chocolate chips.
Press the stiff dough into the baking dish. Bake 8-10 minutes, until almost done. Remove from oven and let cool.