In a medium sized mug (at least 11 ounces), whisk together all dry ingredients. Be sure not to pack in the flour, just scoop it lightly.
Whisk in the wet ingredients, but leave out the marshmallows and chocolate chips for now.
Whisk in 1 tbsp of chocolate chips. Take half of the large marshmallow and cut it into 3-4 smaller pieces.
Whisk in the chocolate chips and marshmallows so they are well combined with the rest of the ingredients.
Microwave on high for 60 seconds, then add the other large marshmallow on top (as is, no need to break it up), and microwave for 20 more seconds.
Let sit for about 3 minutes before eating.