In a medium sized mug (be sure it is microwave safe), add the vegetable oil, egg, milk and whatever flavoring you are using. Mix up these ingredients until well combined.
Add the flour, sugar, cocoa powder and salt. Again mix until well combined. If you are using any of the suggested add ins, now's the time to add them.
Cook in the microwave on high for about 2 1/2 minutes depending on your brand of microwave. The end result should look like the photo at the top.