Combine the graham cracker crumbs and melted butter in a small bowl. Stir until evenly coated and set aside
Pour the cold heavy whipping cream into a large mixing bowl. Add the sugar, vanilla extract, and salt
Beat with an electric mixer until the mixture becomes thick and reaches soft peaks. Do not overwhip
Gently fold the marshmallow fluff into the whipped cream mixture.
Fold in the chopped peanut butter cups, distributing them evenly.
Transfer the mixture to a prepared ice cream maker and churn according to the manufacturer's instructions.
Add the buttery graham cracker crumbs toward the end of churning so they remain in distinct pieces
Transfer the churned ice cream to an airtight freezer-safe container.
Add extra peanut butter cup pieces or graham cracker crumbs on top, if desired.
Cover tightly and freeze for at least 4 to 6 hours, or until firm enough to scoop.