Preheat oven to 350°F. Line a 9x13” pan with foil and spray with cooking spray.
Place the two baking chocolates and butter in a large, microwave safe bowl. Heat on HIGH power for 2-3 minutes, stirring every 30 seconds, until chocolate is smooth. Stir in sugar. Add eggs, vanilla, 1 teaspoon cinnamon, 3/4 teaspoon cayenne, salt, and 2 tablespoons cocoa and stir well. Add flour and stir carefully. Stir in mini chocolate chips.
Spread brownie batter in prepared pan. Bake for 20-25 minutes, until a toothpick comes out with just a few crumbs stuck to it. Let them cool completely before slicing into squares.
Whisk powdered sugar, 1/4 teaspoon cocoa, 1/4 teaspoon cinnamon, and a pinch (up to 1/8 teaspoon) cayenne pepper. Sprinkle over sliced brownies.