One cup roasted, lightly salted peanuts (optional)
Heat oven to 350°F. Line a 8×8-inch baking pan with foil, or parchment paper. Leave a 2-inch flap on two sides, and spray with cooking spray.
Melt butter in a medium saucepan-over medium-low heat. Remove from heat; using a whisk, beat in cocoa powder until smooth—cool 5 minutes.
Add sugar; mix to combine. Then add eggs and vanilla-mix until incorporated. Next, add flour, baking powder, baking soda and salt. Stir until the mixture is moist.
Pour batter in the prepared pan.
Bake for 45 to 50 minutes or until the center of brownies domes and begins to crack, and the toothpick inserted 2 inches from the edge comes out with a few moist crumbs. Allow brownie to cool in pan on a cooling rack, about 2 hours. Refrigerate uncovered 30 minutes.