Step 1

In a saucepan over medium heat, melt marshmallows with milk. Stirring frequently, continue until mixture is completely melted and smooth. Set aside to cool for about 5 minutes.

Step 2

In a mixing bowl, beat butter and shortening until creamy. Add in vanilla and cooled/melted marshmallows. Beat to combine.

Step 3

Gradually add in 2 cups of powdered sugar and beat until creamy. If needed, add up to another 1/2 cup of powdered sugar, until desired consistency is reached.

Step 4

Keep any leftovers in a covered container in refrigerator. When using leftovers from the refrigerator, let the frosting come to room temperature before using.