Does anyone know of a peanut butter cake filling that isn't too sweet and doesn't need refrigeration?

I've found a lot of recipes that look like they need to be kept cold, and I'll be using it in the top layer of a fondant covered cake, so I don't want put it in the fridge after it's been covered.

Any help would be awesome, thanks in advance.

A simple filling is mix the peanut butter with powdered sugar and enough liquid to make it spreadable. It's still sweet, but then again, it is icing. You can add a little salt disolved in your liquid to cut the sweetness. I've always used milk, but it was for that same day. The sugar may cook the milk enough to let it keep well for a few days, but the experts on this site will have to help with this.

I'd be filling it on friday for saturday afternoon, if that helps at all.

You can do a peanut butter buttercrem-- add some salt and use all natural PB--it isn't as sweet as the regular stuff!