1/2 lb. (2 sticks) unsalted butter, room temperature
1/2 lb. powdered sugar
1/2 Tbsp. vanilla extract
1/2 jar Marshmallow Fluff (about 2 cups)
In large bowl of a mixer, cream the butter until soft. Add powdered sugar and vanilla and whip until smooth. Add marshmallow fluff and continue to mix until the frosting is fluffy, about 1 minute.