Allow the cream cheese and eggs to reach room temperature and preheat oven to 350 with oven on upper middle rack.The ideal brownie mix for this recipe is a family sized box, just because you get more ;)
Follow the directions preparing the batter as noted, ignore the baking directions on the box. To the batter, add the mini marshmallows and 1 tsp of vanilla extract and stir one last time.
Add the graham cracker crumble to the bottom in of a buttered and floured or sprayed, nonstick 13x9 cake pan; pour in the brownie batter, set off to the side to prepare cheesecake topping.
Whip the cream cheese until fluffy, about a 1 minute. Then add the remaining teaspoon of vanilla, the last egg and 2 tbsp sugar. Whip for another minute or so until all lumps are gone and it returns to it's fluffy texture.
Scoop the cheesecake mixture with a large spoon or piping bag and make 5 stripes of cheesecake, then microwave the peanut butter until liquid (about 15 seconds depending on your microwave).
Drizzle the PB lightly over top of the cheesecake and also right onto the brownie batter, swirl with a knife or the blunt end of a skewer.
Bake for 30-35 minutes or until cheesecake topping starts to lightly brown and center is barely gooey. Then let the brownies set for about 30 minutes prior to serving.