Choose the right mug: Use a microwave-safe and oven-safe ceramic mug that holds at least 12 ounces. This gives the cake room to rise.
Preheat the air fryer: Set it to 330°F (165°C).
Preheating helps the cake rise evenly and bake on time.
Mix dry ingredients: In the mug, add flour, sugar, baking powder, and a pinch of salt. Stir with a fork until well combined and no streaks remain.
Add wet ingredients: Pour in milk, oil, melted butter, and vanilla. Stir until the batter is smooth.
Scrape the bottom and sides so no dry pockets hide.
Add optional mix-ins: Fold in chocolate chips, sprinkles, or a dash of cinnamon if you like.
Air fry: Place the mug carefully in the air fryer basket. Cook at 330°F (165°C) for 8–10 minutes. Start checking at 8 minutes.
Check doneness: The top should look set and spring back lightly when touched.
A toothpick inserted in the center should come out with a few moist crumbs, not wet batter.
Cool briefly: Let the mug cake rest for 2–3 minutes. This sets the crumb and keeps it tender.
Finish and serve: Top with a dollop of whipped cream, a dusting of powdered sugar, or ice cream. Enjoy warm.