In a large microwave-safe mug*, stir together the flour, sugar, cocoa powder, baking soda, salt, and cinnamon.
Add the milk, butter, and vanilla, and stir until smooth and combined. Mix in the chocolate chips.
Place the mug on a microwave-safe plate, and microwave on high for 1 minute 40 seconds or until the cake is cooked in the middle. (Timing is based on my 800W microwave so your timing might vary. See Recipe Notes below.**)
Enjoy warm with a scoop of ice cream or your favourite toppings!
*You want a big enough mug that the cake batter fills up just over half way.
**All microwaves are different and can yield different results (like an overcooked mug cake). My microwave is 800W and I cooked mine on 100% power for 1 minute 40 seconds. Knowing this may help you better judge how long to cook yours for.
Microwave Watt Time Estimates:
700W - 1min 50sec / 800W - 1min 40sec / 900W - 1min 30sec / 1000W - 1min 20sec
For a more molten effect, cook for 15 - 20 seconds less.
The calories are an estimate only.