Choose the right mug. Use a microwave-safe mug that holds at least 12 ounces. This gives the batter room to rise without spilling over.
Mix the dry ingredients. Add 1/4 cup all-purpose flour, 2 tablespoons sugar, 2 tablespoons unsweetened cocoa powder, 1/4 teaspoon baking powder, and a small pinch of salt to the mug. Whisk with a fork until no streaks remain.
Add the wet ingredients. Pour in 3 tablespoons milk, 2 tablespoons neutral oil (or melted butter), and 1/4 teaspoon vanilla extract. Stir until the batter is smooth and glossy, scraping the bottom corners of the mug.
Stir in extras. Fold in 1 tablespoon chocolate chips for pockets of melty goodness. You can also press a few chips on top for a prettier finish.
Microwave in short bursts. Cook on high for 45 seconds, then check. Continue in 10–15 second bursts until the top looks set and slightly glossy. Total time is usually 60–90 seconds, depending on your microwave’s power.
Let it rest. Allow the cake to sit for 30–60 seconds. It finishes cooking as it rests and becomes a touch fluffier.
Top and serve. Enjoy as-is, or add a scoop of ice cream, a dollop of whipped cream, a drizzle of chocolate sauce, or a few berries.
