Preheat your oven to 350°F (175°C) and grease a 9x13 inch baking pan.
In a large mixing bowl, whisk together the cocoa powder, flour, sugar, baking powder, salt, cinnamon, and cayenne pepper until well combined.
In a separate bowl, mix the melted butter, eggs, and vanilla extract until smooth.
Pour the wet ingredients into the dry ingredients, stirring until just combined; do not overmix.
Gently fold in the semi-sweet chocolate chips and nuts (if using).
Pour the batter into the prepared baking pan, spreading it evenly.
Bake for 25-30 minutes or until a toothpick inserted in the center comes out with a few moist crumbs.
Allow the brownies to cool in the pan for about 10 minutes, then transfer to a wire rack to cool completely.
Once cooled, dust with powdered sugar for a beautiful finishing touch.
Notes
Cut the brownies into squares and serve them on a decorative plate. Add a dollop of whipped cream on the side and sprinkle with extra cinnamon for a beautiful presentation.