Incorporating peanut butter into a porter recipe can be done by using peanut butter powder or a prepared product specifically designed for brewing, such as PB2. Be cautious when using real peanut butter, as the oil content could hinder head retention and cause off-flavors. Add the peanut butter powder during the boil or during secondary fermentation to impart a smooth, nutty flavor to your porter. Start with a small amount and adjust according to taste, keeping in mind that excessive peanut butter could overpower the other flavors in the beer.