Preheat the Oven:
Preheat to 350°F (175°C).
Line an 8x8-inch or 9x9-inch baking pan with parchment paper or grease lightly.
Make the Brownie Batter:
In a large bowl, mix melted butter and sugar until smooth.
Add eggs and vanilla, beating until glossy.
Stir in cocoa powder, flour, salt, and chocolate chips (if using) until just combined.
Make the Peanut Butter Cheesecake Layer:
In a separate bowl, beat cream cheese, peanut butter, and sugar until smooth.
Add egg and vanilla, mixing until creamy and well blended.
Assemble the Brownies:
Pour most of the brownie batter into the prepared pan (reserving about ¼ cup for swirling).
Spread the peanut butter cheesecake mixture evenly over the brownie base.
Dollop the reserved brownie batter on top and swirl gently with a knife or toothpick.
Bake:
Bake for 30–35 minutes, or until the center is set and a toothpick comes out with moist crumbs.
Let cool completely in the pan before slicing.
Serve & Enjoy:
For clean cuts, chill brownies for 30 minutes before slicing. Store in the fridge for up to 5 days.