Preheat oven to 350°F (175°C) and line a 9x9 baking pan with parchment paper.
In a bowl whisk together flour, cocoa powder, cinnamon, cayenne pepper, and salt.
In another bowl mix melted butter and sugar until smooth.
Add eggs, egg yolk, and vanilla extract. Whisk until thick and glossy.
Slowly mix the dry ingredients into the wet mixture until just combined.
Fold in chocolate chips.
Spread batter evenly into the prepared baking pan.
Bake for 22–26 minutes until the center is just set.
Allow brownies to cool for 20 minutes before slicing.