Choose the right mug. Use a microwave-safe mug that holds at least 12 ounces. This gives the cake room to rise.

Mix dry ingredients. Add flour, sugar, cocoa, baking powder, and salt to the mug. Stir with a fork until evenly combined and no cocoa clumps remain.

Add wet ingredients. Pour in milk, oil, and vanilla. Stir until the batter is smooth and reaches the corners of the mug. Scrape the bottom to catch dry pockets.

Add chocolate chips. Sprinkle them on top or fold them in for a molten center.

Microwave. Cook on high for 60 to 90 seconds. Start with 60 seconds; if the center looks wet, add 10–15 seconds at a time. It should rise and look set on top but still moist.

Rest briefly. Let it sit for 1–2 minutes. The cake finishes cooking and the texture improves.

Top and enjoy. Add ice cream, yogurt, or a drizzle of peanut butter. Eat warm straight from the mug.