I used Smooth peanut butter from Fix and Fogg, which is a NZ company who recently opened in the US too and they make the BEST peanut butter. It is more on the 'natural' side so just make sure you give what you are using a really good mix before you add it in, and don't use anything that separates out really badly. The creamy stuff from the store works great here too! You could probably actually use crunchy too and you would get a crunchy filling.... I may need to test this because it sounds so good.