Gather your supplies.
Combine flour, sugar, salt, and cocoa powder in mug. Mix them together until the mixture looks homogenous.
Add the milk, oil, and egg to the mixture. Then stir it together.
It should look like this, a homogenous, smooth cake batter.
Break Break chocolate up in to little pieces. This step can be avoided if you choose to use chocolate chips instead.
Add the chocolate to the mixture and mix it in. If there is extra chocolate you can keep it to sprinkle on top.
Put in microwave for 1 minute and 30 seconds.
Take it out of the microwave and add whatever you want on top of it. Perhaps the leftover chocolate?
Eat it right away, when it's still warm.