Prepare a 9X13 baking pan by lining it with parchment paper and preheat oven to the temperature recommended on the box mix.
Prepare the brownie mix according to the directions on the package. Bake for the recommended time and allow them to cool.
While the brownies are cooling, prepare the peanut butter layer. With a hand mixer, beat the powdered sugar, peanut butter, butter, vanilla and salt until smooth. This will end up as a thick, playdough like consistency. Set aside.
To make the ganache topping, place the 2 cups of semi-sweet chocolate in a medium to large bowl, that you can cover with a lid or a plate, and set aside.
Melt the butter over medium heat in a small saucepan. When the butter is melted, stir in the cream. Whisk this together constantly while increasing the heat to medium high. Cook this mixture until it just starts forming bubbles.
As soon as the butter and cream start bubbling, immediately, pour the cream mixture over the bowl of chocolate and cover it with the lid. Let this sit for five minutes. After five minutes, stir to combine the chocolate and cream mixture. It may take a minute or two of stirring, but you should create a smooth ganache. It may thicken as it cools, which is fine, just give it a stir.
Once the brownies have cooled, top with the peanut butter mixture by scooping out spoonfuls of the mixture onto the brownie layer, then use a spatula to smooth out and cover the brownie layer completely.
Pour the ganache on top of the peanut butter mixture and smooth with a knife or offset spatula.
Place the brownies into the fridge to allow them to cool and set for easier cutting. They will need at least 30 minutes to chill.