01 -
Heat up your oven to 350°F (177°C). Pick either a 9×9-inch or 9×13-inch pan depending on how thick you want it. Set it aside after prepping.
02 -
Stir together melted butter (113 g), 1 egg (put the other 2 eggs aside for later), and the cake mix. Blend well, press it flat into your pan, and leave it for now.
03 -
Use a hand mixer or a stand mixer to whip up the cream cheese until smooth. Toss in the rest of the eggs and add the peanut butter. Keep mixing until it all looks blended together.
04 -
Set the mixer to low speed. Add in the powdered sugar bit by bit, followed by the remaining stick of melted butter. Pour in the vanilla and stir until the batter is smooth.
05 -
Pour the filling over your base in the pan. Pop it in the oven and bake for 50 minutes. The middle should still look a little soft—don't overdo it.
06 -
Place the pan on a wire rack and let it cool slightly while you whip up the ganache.