Break chocolate bars up and melt in a microwave-safe bowl at 30-second intervals, stirring between each segment until it’s completely melted; approximately 90 seconds total. Set aside to cool.

In a stand-up mixer, beat the butter until smooth. Add the cooled chocolate and Marshmallow Creme to the butter and mix on medium speed.

Gradually add in the powdered sugar one cup at a time with 1 tablespoon of milk. Add enough of each to get a fluffy frosting consistency.

Use an offset spatula to spread the frosting onto a cake or transfer it to a piping bag for cupcakes.