I actually split my brownie mix between two pans and tried these two separate ways- topped with Reeses before baking, and topped with Reeses right after baking. EVERYONE went for the brownies topped post-baking, but tasting them blind- the baked-in version won every time. So you really have to decide if you want pretty brownies or yummy brownies. Unless you feel like compromising and doing both that is...
This is one of my anti-recipes. Like there really is no recipe. There's just a method. But I'll share it with you anyways. First chop up a bunch of Reese's Peanut Butter Cups. Maybe 10 or 16. I don't care how many.
Your garbage can should look like this:
Pour batter into a pan and top with Reeses chunks.
Bake brownies according to package instructions without addition of delicious chocolate peanut butter candies. When done, remove from the oven, and immediately top with Reeses chunks. Allow to melt for a few minutes, then chill in freezer until very cool before cutting. Return to room temperature before eating.
These do not keep well. They tend to dry out much faster than regular brownies so I recommend eating them day-of for maximum deliciousness.