Take a microwave-safe mug and add the all-purpose flour, granulated sugar, baking powder, and salt. Mix the dry ingredients thoroughly with a small whisk until well combined.
Add the milk, vegetable oil, and vanilla extract to the dry ingredients. Stir the mixture with a spoon or small whisk until smooth and no lumps remain.
If desired, gently fold in some sprinkles to give the cake a cheerful and colorful touch.
Place the mug in the microwave and cook the cake on high for 1 minute and 30 seconds. Check the center of the cake after this time; if it is still wet, cook in additional 10-second intervals until fully cooked (microwave times may vary).
Allow the mug cake to cool for a few minutes before enjoying.
Notes
Top with whipped cream, a scoop of ice cream, or extra sprinkles for a delightful treat.