Stir together the hot cocoa powder and milk, until there are no lumps. Set aside.

In a mixer, whip together the butter and marshmallow cream until well combined. Add the sugar, a heaping half cup at a time, mixing between additions and scraping down the sides of the bowl. Once all the sugar is added, put the mixer on low and drizzle in the cocoa mixture.

Slowly turn the mixer up to medium-high speed and whip together for about one minute, until the chocolate is incorporated and the frosting is fluffy.

Give it a taste and add more chocolate, if necessary. Then frost!