Prepare the brownies. Preheat the oven to 350 degrees. Grease an 8 x 8 inch baking dish with butter or if you want to be able to remove and serve your brownies outside of the pan, create a parchment paper sling. Set aside.

In a medium sized pot, melt the butter on the stove top over medium heat. Remove from heat, then whisk in brown and white sugar until smooth and creamy, about 1-2 minutes.

Add the eggs and egg yolk, one at a time, whisking well after each addition. Stir in the vanilla and salt.

Add the cocoa powder and flour and stir until just combined. Pour the mixture into the prepared pan and bake for 33-39 minutes (underdone, our recommendation) or 40-45 minutes (baked through). We take it out with the center is just set and no longer jiggly. Allow the brownies to cool.

Meanwhile, make the filling. Place butter and peanut butter in the bowl of an electric mixer. Beat with the paddle attachment until smooth and creamy.

Add powdered sugar in two additions, beating well after each addition. Stir in vanilla. Spread the frosting evenly over the cooled brownies.

Meanwhile, make the chocolate coating. Place the chocolate and coconut oil in a heat proof bowl and microwave in 30 second increments, stirring after each one, until melted and smooth. Spread the chocolate over the peanut butter filling, gently spreading it all the way to the edges. Sprinkle with sea salt. Allow to set up before slicing and serving, approximately 1 hour in the refrigerator or several at room temperature.