Preheat oven to 350F. Spray a 8x8-inch baking dish with non-stick cooking spray, then line with parchment paper; set aside.

In a medium saucepan, melt the butter over medium heat. Turn off the heat then add ½ cup of chocolate chips and whisk until melted.

Pour the chocolate mixture into a large mixing bowl and set aside to cool for a few minutes.

Add the granulated sugar, brown sugar, eggs, and vanilla extract to the chocolate mixture and stir well to combine.

In a small mixing bowl, combine the flour, cocoa powder, and salt. Stir the flour mixture into the wet ingredients until combined.

Fold the remaining ½ cup chocolate chips into the brownie batter.

Scoop the brownie batter into the prepared baking dish.

In a microwave safe bowl, melt the peanut butter in the microwave for 20-30 seconds on high. Pour the melted peanut butter over top of the brownie batter and use a butter knife to swirl it slightly into the batter.

Bake the brownies at 350F for 40-50 minutes until the center is set.

Cool the brownies completely before slicing.