Delicious, rich, decadent peanut butter filling. You could eat this straight out of the bowl.
This makes enough for one generous layer in a 9-inch cake.
In the bowl of a mixer, beat butter until soft and fluffy. Add peanut butter and mix well. Gradually add sifted powdered sugar, beating until well-incorporated.
If the peanut butter is really cold, it's best to warm it in the microwave slightly.