In a stand mixer fitted with a paddle attachment, beat the softened butter on medium speed. With the mixer on low, slowly add the powdered sugar 1 cup at a time. Mix until fully incorporated.
Add the vanilla extract and salt and mix on medium speed until blended.
Add the marshmallow fluff and mix on medium speed until combined.
With the mixer running on slow speed, slowly add the heavy whipping cream. Increase to medium-high speed and mix until light and fluffy.
Keyword A marshmallows frosting perfect for Smores cupcakes