Preheat the oven to 350°F. Line a 9x9 inch baking dish with parchment paper, and lightly spray with nonstick spray.

In a small bowl, whisk together the flour, cocoa powder, baking powder, and chocolate chips.

In a medium bowl, add melted and cooled butter.

Add granulated sugar, light brown sugar, eggs, vanilla, and salt. Stir until combined.

Stir in the flour mixture and chocolate chips just until combined, avoiding overmixing.

Spread half of the batter into the prepared pan.

Dollop teaspoons of ⅔ cup peanut butter over the batter.

Spread remaining batter over the peanut butter dollops.

Warm remaining ⅓ cup peanut butter for about 10 seconds in microwave and stir.

Drizzle the warmed peanut butter over the batter and create a swirl pattern.

Bake for 30 minutes, until a toothpick inserted comes out with moist crumbs.

Cool completely for 2 hours before cutting into slices and serving.