Preheat oven to 350 degrees (or as directed on brownies).
In large mixing bowl, prepare brownie mix as directed and set aside.
In medium sized mixing bowl, beat cream cheese for 1 minute or until smooth. Add in peanut butter and continue mixing until smooth.
Add in sugar, egg, flour, and vanilla and mix until well combined and creamy.
Pour all but 1/2 cup of brownie batter into a 9x13 glass baking dish, that has been well coated with non-stick cooking spray.
Spoon peanut butter cream cheese mixture in dollops on top of the brownie mixture and lightly spread.
Spoon the rest of the brownie batter on top and using a knife begin swirling the batter drawing vertical and horizontal lines. Have fun creating the marbled effect here- you really can't mess this part up!
Bake in preheated oven for 35 minutes or until a toothpick comes out clean.
Once fully baked, remove from oven and let cool before cutting into bars.