I have a chocolate cake with peanut butter filling order.  Can I add peanut butter to the Costco filling?  If I can, at what point do I add the peanut butter?

Thanks in advance.

why don't you make a small batch of it, like maybe 1/2 a cup of the Costco filling and a few tablespoons of peanut butter and let me know if it worked.  Good luck.