In the bowl of a stand mixer, beat the butter until creamy.
Add the sugar and beat until creamy, then add the vanilla.
Add the Marshmallow Fluff (or Marshmallow Creme) and beat until fluffy.Put in a piping bag and pipe on top of cupcakes
In my opinion, it worked the best on cupcakes. It was fine on a layer cake, but the texture isn’t as smooth when spread and it seems to work better when piped out in dollops.