Preheat oven to 300 degrees F
Butter a 13-by-9-inch baking pan. Line pan with parchment paper, leaving a 1-inch overhang on 2 sides.
Melt butter in microwave-safe bowl. Add cocoa powder to melted butter and stir thoroughly.
In a large bowl, combine sugar, cinnamon and cayenne pepper. Using a wooden spoon, stir in cocoa and butter mixture. Add eggs 1 at a time, beating until just combined. Stir in vanilla. Mix in flour and salt in 3 additions, stirring until just combined. Mix in chocolate chips. Pour into prepared pan.
Bake until cake tester inserted in the center comes out with only a few moist crumbs, 35–40 minutes. Transfer pan to a wire rack to cool completely. To make for easier cutting, chill brownies for about 1 hour.