To add a little kick to these brownies, lightly brown 2 cups hazelnuts in 2 tablespoons peanut oil. Let cool, then remove the skins by rubbing the nuts in between a clean dish towel. In a food processor, pulse the nuts until they are slightly crumbled, then add the cocoa powder and the chili powder and pulse until fully incorporated. Transfer to a bowl and set aside.
Preheat the oven to 350 degrees F.
Line an 8 by 8-inch baking pan with parchment paper leaving a 2-inch overhang to use as handles for removal.
Add the butter and chocolate to a medium-sized saucepan over medium heat, stirring to melt. Once melted and smooth, remove from heat. Whisk in the sugars. Add the eggs, 1 at a time, stirring between additions, then add the vanilla extract.
Whisk together the cocoa powder, flour, baking powder and salt, if using, in a separate bowl. Add the dry ingredients to the chocolate mixture and stir well.
Fold in 1 1/2 cups of the hazelnut mixture. Pour the batter into the prepared pan and spread evenly. Sprinkle the top with the remaining 1/2 cup of hazelnut mixture and bake for 20 to 30 minutes. Remove the brownies from the oven, and cool to room temperature. Cut into squares and sprinkle with confectioners' sugar before serving.