For filling:1 stick unsalted butter, softened1 1/4 cups confectioners sugar 2 cups marshmallow cream 1 teaspoon vanilla
Filling:
Beat butter, confectioners sugar, marshmallow, and vanilla in a bowl with a stand up or hand held mixer on medium speed until smooth and creamy, for about 3 minutes.
Assemble:
Dollop a tablespoon of filling on the flat sides of half of cakes and top with the remaining cakes.
Lastly, enjoy!