Choose a microwave-safe mug that’s at least 10–12 ounces in size — the cake will rise as it cooks, and you don’t want it to overflow.
Add flour, cocoa powder, sugar, baking powder, and a pinch of salt directly into the mug. Stir them together with a fork or spoon until the mixture looks smooth and uniform.
Pour in the milk, oil, and vanilla extract. Stir gently until everything is fully combined. The batter should be smooth but slightly thick — like a typical cake batter.
Place the mug in the center of the microwave and cook on high for 60–75 seconds. Cooking time depends on your microwave — start with 1 minute, then check.
The cake should rise slightly above the rim and look set on top but still soft inside. If it’s still a little wet in the middle, microwave for another 10 seconds.
Take the mug out carefully — it will be hot! Let it sit for a minute or two.
