I adore the texture of this frosting. It is truly one of the lightest and fluffiest buttercreams I have ever made.
Cream butter in a mixing bowl with an electric mixer on medium until butter is light and fluffy. (Can also use a stand mixer with paddle attachment.) About 2 minutes.
Gradually beat in confectioners' sugar, about a 1/2 cup at a time. Once all is added, mix on high for 2-3 minutes.
Once fully combined, gently fold the marshmallow creme into the frosting by hand. Can be used immediately or refrigerated until ready to use.