Preheat the oven to 350 degrees. Butter a 9-by-13-inch baking pan.
Place the chocolate and butter in a medium saucepan and melt over low heat, stirring until smooth, about 5 minutes. Remove the chocolate from the heat and whisk in both sugars until smooth.
In a resealable plastic bag, combine the flour, cocoa powder, chili powder, baking powder and salt and shake together to mix. Whisk the eggs, 1 at a time, into the barely warm chocolate mixture. Add the flour mixture and stir until smooth. Pour the brownie mixture into the prepared pan and bake until set, about 25 minutes. Let cool 5 minutes, then cut the brownies into desired shapes with a cookie cutter or knife. Serve warm with a scoop of ice cream and the chocolate curls.