In the bowl of a stand mixer fitted with the paddle attachment or a large mixing bowl with an electric hand mixer, cream together the cream cheese and peanut butter until smooth.
Add the instant pudding mix, blending again, then pour in the heavy cream. The mixture will start out globby, but as the cream whips, will come together.
Blend in the marshmallow fluff and powdered sugar.
By hand, fold in the mini Reese's mini peanut butter cups, reserving a few to garnish the top.
Serve with your favorite dippers.
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Notes
This dip can be made ahead and stored in an airtight container in the refrigerator for up to three days.