01 -
Get your oven hot at 350°F (175°C). Coat a 9×13 inch pan with grease and flour.
02 -
Take a medium bowl and stir the flour, baking powder, baking soda, and salt together. Put it aside for now.
03 -
In a big bowl, beat the butter, peanut butter, white sugar, and brown sugar until it's airy and pale.
04 -
Drop in eggs one by one, then mix in the vanilla.
05 -
Add the flour mix bit by bit to the butter mix, switching with buttermilk. Start and finish with flour. Just mix enough to blend it all.
06 -
Dump the mix into your ready pan and even it out. Cook for 30-35 minutes. It's done when a stick poked in the middle comes out clean.
07 -
Put the pan on a wire rack and wait till the cake is totally cool.
08 -
For your topping, whip the butter with peanut butter till smooth. Slowly add sugar, milk, and vanilla. Beat until it's fluffy and light.
09 -
When cake is cool, spread the topping all over. Cut and enjoy.