Preheat oven to 350 degrees F. Grease a 9x13" pan. Melt butter in a non-stick saucepan over medium-low heat, making sure not to boil. Remove from heat and let cool slightly. To the saucepan, add the sugar and the eggs. stir with a wooden spoon until creamy. Add in the cocoa powder, flour, cinnamon, cayenne, salt, and baking powder. Mix until a smooth texture. Spread batter into pan and bake for 20 minutes.