Mix all of the ingredients except for the chocolate chips together for the hot chocolate mug cake mix and whisk until well combined. Place the chocolate chips in a separate container.
To make a mug cake, take ¼ cup, plus 2 teaspoons of the mix and a tablespoon or two of the chocolate chips (depending on how chocolaty you want it!) and pour into a microwave-safe mug that holds at least 10 oz. Stir in milk and oil and mix until smooth.
Microwave for 60 seconds. Top with marshmallows and dig in!