In a large microwave-safe mug, stir together the flour, sugar, cocoa powder, baking powder, and salt.
Add the milk, oil, and vanilla and stir until well combined and smooth. Stir in most of the chocolate chips, and sprinkle the top with the remaining chips.
Microwave on high for 60 to 90 seconds or until the cake is puffed and the center looks dry. Let cool for a few minutes before eating.
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Notes
Make sure to measure your flour correctly. If you add too much flour to the recipe, you will have a dry mug cake. I highly recommend always using a scale to measure. However, if you don’t have a scale, be sure to fluff your flour with a spoon and then spoon it into your cups before leveling it off with a knife. This method is the best way to measure flour without overpacking the measuring cup.
A shorter, wider mug is ideal as it allows for more even cooking. I recommend a heavy ceramic mug with no metal. If your mug is too small, the batter may overflow.
Just like a regular cake, avoid overmixing the batter, or you’ll end up with a dense, tough cake.
The strength of microwaves can vary, so the first time you make this recipe, you'll need to experiment between 60 to 90 seconds. The thickness of your mug will also contribute to how long it’ll take for it to cook.
Some delicious variations you can make to this mug cake are stirring in a spoonful of cream cheese, caramel, peanut butter, Nutella, or Biscoff into the batter before baking or serving it with a spoonful on top.