Preheat and prepare:
Preheat your oven to 350°F (175°C). Line an 8-inch square baking pan with parchment paper, ensuring some overhang for easy removal later.

Make the chocolate base:
In a medium bowl, combine the melted butter and dark chocolate chips. Stir until fully melted and smooth. Warm in the microwave for 10 to 15 seconds if necessary. Set aside to cool slightly.

Whisk sugar and eggs:
In a separate large mixing bowl, vigorously whisk together the sugar and eggs for 2 to 3 minutes until the mixture is light and frothy.

Combine chocolate and egg mixtures:
Pour the melted chocolate mixture into the egg mixture. Stir gently until well combined.

Add dry ingredients:
Sift in the cocoa powder, gluten free flour, and sea salt. Fold together until just combined, ensuring there are no streaks of flour.

Layer the brownies:
Pour half of the batter evenly into the prepared pan. Arrange the peanut butter cups evenly over the batter.

Prepare peanut butter swirl:
In a small bowl, mix together the creamy peanut butter and powdered sugar until smooth and spreadable. Spread this mixture evenly over the peanut butter cups.

Top and bake:
Pour the remaining brownie batter over the peanut butter layer and smooth the top evenly.

Bake and cool:
Bake for 33 to 36 minutes, or until a toothpick inserted near the center comes out mostly clean with a few moist crumbs. Remove from the oven and allow the brownies to cool completely in the pan before lifting out and slicing into 9 servings.