01 -
Heat up the oven to 350°F (177°C). Get either a 9×9-inch or 9×13-inch pan ready, depending on how thick or thin the cake should be.
02 -
Stir together the cake mix, a single egg (keep the other two eggs for later), and 113 g (1 stick) of melted butter. Press evenly into your prepared pan. Put aside for now.
03 -
Use a hand or stand mixer to beat the cream cheese until it's creamy. Add the last two eggs and smooth peanut butter, mixing them in gently.
04 -
Turn down the mixer speed and carefully add the powdered sugar in steps. Slowly pour in another melted stick of butter (113 g), then mix in the vanilla extract. Stir until silky and lump-free.
05 -
Pour the creamy layer over the base in the pan. Bake for about 50 minutes, leaving the center slightly soft and gooey. Be careful not to overdo it.
06 -
Let the cake chill for a bit on a wire rack while you prepare the ganache topping.