From searching around here, youll find that using actual PB is highly unsuccessful due to the fat content. You get a layer of oil on top of your wort which can mess up fermentation by preventing yeast oxygen exposure when they try to rise to the top.
Most people will use PB2 (defatted PB powder) and/or PB flavor extracts. For my PB stouts, Ive done a box of captain crunch in the mash along with the PB2 and flavoring. Its pretty hard to lock in a good PB flavor