Put back in oven for 3 minutes or until marshmallows puff up and begin to melt. Don't let them brown.
Remove from oven and allow to cool before frosting.
Frosting
Mix all frosting ingredients together and spread over cake.
Video
Notes
How to Cut:Because of the warm marshmallow layer, they can be tricky to cut. They are more difficult to cut when they are warm but they are so yummy warm! So if you don't care what they look like, just grab a knife and cut into them right out of the oven. They will taste like heaven, but you'll have a nice chocolate marshmallow mess. If you would like a nice clean cut, refrigerate them first and then cut. You can serve them chilled or room temperature.