I did mine with the peanut butter in the boil for the entire boi. I did not add any other peanut butter or flavoring. the aroma was like sniffing the top of a freshly opened jar of peanut butter and the flavor was perfect. I do not think that anything in peanut butter is fermentable, or if it is, it did nothing but good for my beer. I plan to make it the same way again, only use PB2 instead of real peanut butter. The oil did kill a lot of the head, but it still has some, and I skimmed as much of it off as I could during the boil.