Mix the Dry Ingredients: In a microwave-safe mug or small bowl, whisk together the flour, granulated sugar, cocoa powder (if using), baking powder, and salt. Whisk until there are no lumps.
Add the Wet Ingredients: Add the milk, vegetable oil (or melted butter), and vanilla extract to the dry ingredients. Stir until the mixture is smooth and combined. Be careful not to overmix.
Microwave: Place the mug in the microwave and cook on high for 1–1.5 minutes. The cake will rise as it cooks. It should be firm to the touch but still moist. Avoid overcooking, as this can dry out the cake.
Cool and Decorate: Let the cake cool for a minute or two. Then, add your favorite toppings, such as a dusting of powdered sugar, a drizzle of chocolate, or a dollop of whipped cream.
Enjoy! Grab a spoon and enjoy your warm, freshly made cake. It’s best served immediately!
