In a microwave safe bowl, combine margarine, brown sugar, and marshmallows. Cook at 1 minute intervals in the microwave, stirring between each interval, until the mixture is melted and smooth. Stir in the peanut butter until well blended.
Pour the brown sugar mixture over the popcorn, and stir quickly to coat the corn before it cools.
Peanut Butter Popcorn · Dinner Match Lab | Dinner Match Lab