Preheat oven to 350 degrees. Line 8 x 8 inch cake pan with parchment paper and allow paper to hang over the sides of the pan for easy lifting
In a mixer bowl combine the peanut butter swirl ingredients or the cream cheese swirl ingredients. Beat on low 10 seconds to combine. Increase speed to medium and beat about 1-2 minutes or until smooth. Set aside
In a medium microwave safe bowl combine the 8 TBS of butter and the chocolate chips. Microwave on high 30 seconds. Stir to combine. Continue to microwave in 15 second intervals until chips and butter are fully melted and combined. Be sure to stir after every interval. The mixture will be very thin. Set aside
In a large mixing bowl sift or whisk together the dry ingredients until there are no lumps. Add the eggs and stir until all the dry ingredients are moistened
Add oil and vanilla. Stir until fully combined and a thick batter has formed. Add the chocolate/butter mixture to the batter and stir until fully combined and smooth
Spread about 3/4 of the batter evenly into the bottom of the prepared cake pan. Spread about 3/4 of the peanut butter or cream cheese swirl evenly over the chocolate batter
Drop the remaining chocolate by tablespoon full over the peanut butter. Use a knife to swirl the chocolate into the batter
Drop the remaining peanut butter over the batter and use a knife to swirl the peanut butter into the batter so that both colors can be seen
Place in preheated oven and bake 25-30 minutes or until a tester comes out clean
Remove from the oven. Allow to cool in pan for at least 1 hour or until firm enough to remove
After 1 hour. Grasp the parchment paper and carefully lift the brownie slab out onto a cutting surface. Allow to cool completely and cut into desired pieces. Serve immediately or store leftovers in an airtight container at room temperature up to 1 week