For the Brownies
For the Peanut Butter Filling
For the Ganache Topping
Preheat oven to 350°F. Butter the bottom and sides of an 8x8 inch baking pan. Put a long piece of parchment paper in the bottom of the pan, letting the parchment extend up two sides of the pan and overhang slightly on both ends. (This will make it easy to remove the bars from the pan after they have baked)
In the bowl of a stand mixer fitted with the paddle attachment, and add the butter, sugar and vanilla. Mix to combine. Beat in eggs one at a time. Mix in cocoa, baking powder and salt. Add flour and mix until just combined and no streaks of dry ingredients remain. Pour into prepared pan and spread into an even layer. Bake for bake 45-60 minutes. Let cool completely in pan on a cooling rack.
While the brownies are cooling, make the peanut butter filling. In the bowl of a stand mixer fitted with the paddle attachment, combine the ingredients and beat until smooth. Spread in an even layer over the cooled brownies. The filling is a thick consistency. You may find it most helpful to use your hands to spread the filling evenly.
Make the ganache topping. Melt together chocolate chips and butter over low heat until smooth, stirring constantly. Pour the ganache over the brownies and spread evenly. Let set before cutting and serving.