Prepare the Batter:

In a microwave-safe mug or small bowl, whisk together the self-rising flour, ground cinnamon, granulated sugar, and salt until well combined.

In a separate bowl, mix the melted and cooled butter, milk, and vanilla extract.

Pour the wet ingredients into the dry ingredients, stirring until you achieve a smooth, lump-free batter.

Make the Cinnamon Sugar Topping:

In a small bowl, combine the granulated sugar, brown sugar, and ground cinnamon. Mix thoroughly.

Assemble the Mug Cake:

Spoon half of the batter into the mug.

Sprinkle half of the cinnamon sugar topping over the batter.

Add the remaining batter on top.

Finish by sprinkling the rest of the cinnamon sugar mixture over the surface.

Microwave Cooking:

Place the mug in the microwave and cook on high for 1 minute and 45 seconds to 2 minutes, depending on your microwave's power.

The cake is ready when it has risen and a toothpick inserted into the center comes out clean.

Cool and Enjoy:

Carefully remove the mug from the microwave—it will be hot!

Allow the cake to cool for a couple of minutes before indulging.