In a small bowl, add all of the ingredients and mix well with a whisk. Pour into 2 large mugs.
When ready to serve, place one mug at a time in the microwave for 90 seconds up to 2 minutes, or until a toothpick comes out clean when placed in the center of the cake.
Add toasted marshmallows on top and drizzle with hot fudge sauce.
While cooling, cook the other mug of cake.
Allow it to cool for one to two minutes before eating.