Melt Chocolate: Melt the dark chocolate and coconut oil together in a double boiler over low heat, stirring occasionally, until smooth and glossy. Alternatively, microwave in a microwave-safe bowl in 20-second intervals, stirring between each interval, until melted and smooth. Set aside.
Melt Peanut Butter: Melt the peanut butter and coconut oil together in a small saucepan over low-medium heat until smooth. Alternatively, microwave in a small microwave-safe bowl for 10–15 second intervals, stirring between each interval, until smooth and easy to drizzle.
Add Melted Chocolate: Pour the melted chocolate over the chilled brownie base. Gently tilt and move the pan in different directions to help the chocolate spread evenly across the surface. If needed, use a spatula to smooth out any areas.
Swirl Peanut Butter: Spoon small dollops of the peanut butter mixture over the chocolate layer. Use a knife or skewer to gently swirl the peanut butter through the chocolate, being careful not to overmix.
Chill: Refrigerate for 3–4 hours or overnight, until the chocolate topping is set and the brownies are firm enough to slice.
Slice and Serve: Remove the brownies from the refrigerator and let them sit at room temperature for 10–15 minutes before slicing. For clean slices, run a sharp knife under hot water for a few seconds, then wipe it completely dry before cutting. The warm knife will help glide through the chocolate topping without cracking. Enjoy!