why my brownies taste bitter?
Unsweetened Cocoa powder is a very bitter ingredient, and 1/2 a cup of it seems like a lot considering the ratios. If you want your brownies less bitter then you may want to reduce the cocoa some, or add more sugar, or do both. Try reducing your cocoa by 2 tbsp and adding 2 tbsp more sugar, adjust the ratios that way until you have the right balance.