Sister Three sent me this recipe...not sure where she got it.  I made it and will make it again but I will make a few changes (I'll let you know how it goes.)  You may want to try the original first to see what you think the link in the title downloads the original recipe.

I used 65% cacao chocolate chips and 70% cacao cocoa so mine was pretty rich.  An extra spoon full of sugar would help balance the bittersweet...but maybe not required if you are using a lower percentage.  I will use just the egg white next time. It was SO rich that the ice cream was truly needed for balance.  No...really...needed!

The changes I plan are in the pdf file on this link but basically I would...

add one extra tablespoon of sugar
use egg white only
chocolate chips are NEVER optional
Don't stir after adding the chips...they will sink by themselves
vanilla ice cream on the side

5 MINUTE CHOCOLATE MUG CAKE

4 tablespoons flour
4 tablespoons sugar
2 tablespoons cocoa
1 egg
3 tablespoons milk
3 tablespoons oil ..or try real butter...worked very well
3 tablespoons chocolate chips (optional)
a small splash of vanilla extract
1 large coffee mug

Add dry ingredients to mug, and mix well. Add the egg and mix thoroughly. Pour in the milk and oil and mix well. Add the chocolate chips and vanilla extract, and mix again.

Put your mug in the microwave and cook for 3 minutes at 1000 watts (high). The cake will rise over the top of the mug, but don't be alarmed! Allow to cool a little, and tip out onto a bowl and add ice cream.

EAT! (this can serve 2 if you want to feel slightly more virtuous). And why is this the most dangerous cake recipe in the world? Because now we are all only 5 minutes away from chocolate cake at any time of the day or night!