I was about to toss the empty flour bag when the word "brownie" jumped out at me. Yeah, I know "who needs ANOTHER brownie recipe?"...those of us who have a cookbook devoted exclusively to chocolate or brownies, that's who! =D
In a medium sized microwave-safe bowl or in a saucepan, melt the butter on low heat, then add the sugar and stir to combine.
Return the mixture to the heat or microwave briefly, just until it's hot but not bubbling. It will become shiny looking as you stir it. Heating the buter and sugar a second time will dissolve more of the sugar, which will yield a shiny top crust on your brownies.
Transfer the mix to a mixing bowl.
Stir in the cocoa, salt, baking powder, and vanilla.
Add the eggs, beating till smooth; then add teh flour and chips and nuts if using. Beat until well combined.
Spoon the batter into the prepared pan.
Bake the brownies for 28-30 minutes, until a cake tester inserted in the center comes out clean or with just a few crumbs clinging to it.
The brownies should feel set both around the edges and in the center.
Remove from the oven, and after 5 minutes loosen the edges with a table knife, this will help preven the brownies from sinking in the center as they cool.