A perfectly balanced brownie (not too fudgy, not too cakey) with a light textured chocolate buttercream frosting.Also, this recipe halves well. To make a half batch, halve all the ingredients and bake in an 8 inch square pan.
Natural cocoa powder is more acidic than Dutch or "Dark" cocoa powder, and its acidity works in conjunction with the alkaline baking soda to affect the leavening process. You could get away with using dark or Dutch, but the brownies may or may not rise quite as much or they may just have a different texture.
For the flour, make sure not to use too much. If you weigh out 6 oz you'll be fine. If you don't have a scale and are measuring by volume, be sure to aerate and stir the flour and measure it without packing it into to cup. Too much flour can make brownies dry.