How much white chocolate should I add to these brownies?

I think the best thing to do with the white chocolate would be to either stir it into the mix before you bake it, or sprinkle the chips on top. If you are going to put them into your brownie, assuming you're going to be cooking it in a 9x9 pan, I would use 3/4-1 cup. If you want to just want to put them on top, you would just pour the mix into the pan, and evenly sprinkle the white chocolate over top of it.