Add all dry ingredients into a microwave-safe mug and mix well until evenly combined for a uniform base.
Pour in milk, oil, and vanilla extract, then stir until a smooth batter forms without visible dry flour.
Fold in optional chocolate chips or coffee for enhanced flavor and richness throughout the cake.
Microwave on high for 60–90 seconds, checking at 60 seconds to avoid overcooking and dryness.
Let the mug cake rest for 1–2 minutes so the texture stabilizes and finishes cooking gently.
Add toppings like ice cream or chocolate drizzle and serve warm directly from the mug.