Preheat oven to 350 degrees. Grease an 8-inch baking pan with coconut oil and line with parchment paper.
Whisk together arrowroot powder, cocoa powder, salt and set aside.
In a large microwave-safe bowl, combine the chocolate chips and coconut oil. Microwave in 30 second intervals, stirring each time, until almost all chips have melted. Stir until smooth and allow to cool for a minute or two before next steps.
Stir in coconut sugar and vanilla. Stir in eggs, one at a time, until combined.
Add arrowroot powder mixture and mix well until combined and smooth.
In a small bowl, combine ingredients for peanut butter swirl and mix well.
Pour batter into pan and smooth top. Drop tablespoons full of the peanut butter mixture on top of batter. Using an offset spatula or butter knife to swirl the batters together in a loose figure-8 pattern. Bake until a toothpick comes out clean, for 30 to 35 minutes, making sure to rotate hallway through.
Let cool completely on wire rack before cutting into squares. Store in an airtight container.