The recipe I have is super easy.
1/2 Cup of room temp. butter
1 Cup of powdered sugar
1 tsp of vanilla extract
7oz Marshmallow fluff
Beat butter and sugar until fluffy, mix vanilla extract and fluff in until incorporated.
It’s supposed to be enough to cover two 8” cakes. I happened to use it for two 6” cakes. It IS a sticky frosting so to work it down around the edges of the cake, I dipped an offset spatula in hot water. I didn’t wipe the spatula off before “molding” the frosting down. Just note, it’s a very sweet frosting. The kids LOVE it.

It worked very well with a darker chocolate cake.