I made these in a 9"x13" pan lined with parchment or wax paper, layer cookie dough, peanut butter cups, and Oreo cookies, and top with brownie batter. I baked them at 350F for 40-50 minutes, until toothpick between Oreos came out clean, but the very middles were still gooey and uncooked.
I think a good solution would be to put the Oreo layer beneath the peanut butter cup layer, or bake it in two smaller pans.
You can customize this any way you like by layering different types of cookie dough, candy bars, and brownie recipes. Go wild! Bake for less time than you think it will take, and just keep checking until everything looks like it's done! But remember, even undercooked brownies are still darn good brownies. Let them cool and use a serrated knife to make clean cuts.