This is absolutely tasty!
MODIFIED FROM THE SITE BELOW!
You can make this recipe doubled and then split it into two mugs to make this recipe a little easier, if you find it difficult to split the egg in half. You can also make the double batch and put the other half in the fridge or freezer to bake later. Although I have not tried it, maybe you can use liquid egg substitute (and I said maybe).... ^-^

1. Put half of an egg into your mug.
2. Add a teaspoon of vanilla extract.
3. Add 3 tablespoons of brown sugar.
4. Add in a tablespoon of milk.*
5. Put in a tablespoon of softened butter or margarine.**
6. Add in 1/3 cup of flour.
7. Sprinkle a pinch of baking powder in.
8. Add in 3-4 tablespoons of mini chocolate chips to top it all off!
9. Mix your cake together with a spoon.
10. Microwave your cake for 1 1/2-2 minutes, or just until the top center of the cake has set. Serve with a dollop of ice cream and enjoy!

* I used whole milk for this, I do not know if other milks would be thick enough for this recipe, but you could try it if you like.
**I used margarine!

*** I also didn't use chocolate chips when testing this(didn't have enough) but when i did try with chocolate chips, they tasted funny.... i will keep modifying it later. Sorry, but without the chocolate chips it tastes good, lol.

This is a modified recipe from this site:
http://blogs.babble.com/family-kitchen/2011/09/20/chocolate-chip-cookie-dough-mug-cake/