You must use a mug suitable for the microwave. 8-ounce mugs that are shorter and wider work better than tall and skinny mugs.

In the mug combine the flour, sugar, baking powder, cocoa, and salt. Using a fork, stir to combine.

Add the milk, oil, and vanilla to dry ingredients and stir well to combine the wet and dry ingredients.

Add 2 tablespoons of the chocolate chips, and 2 tablespoons of the marshmallows. Crush half of the graham cracker and add it to the mug. Stir to combine the ingredients.

Microwave for 60 seconds. Microwaves do cook a little differently from model to model, so cooking times will vary. I started with 60 seconds but if your microwave is more than 700 watts you may want to start with 40 seconds. You can always cook it a bit longer.

Sprinkle remaining graham cracker, marshmallows, and chocolate over mug cake. Microwave for an additional 10 seconds.

Remove from microwave. Let sit for a minute. Garnish with a wedge of chocolate bar and graham cracker crumbs. Serve warm.