Add the dry cake mix; stir well, but don't overbeat. If the batter needs a litle more water, add a teaspoonful at a time. But don't add too much because the batter should be thick. Don't overmix - just mix enough so that there is no "powder" showing.
Pour into the prepared pan, being sure to smooth the top evenly.
Bake for 20 to 25 minutes for chewy brownies; if you like them a little drier, bake a few minutes longer.