Step by step

Method

4 steps

1. 1

   In a microwave-safe mug (about 10–12 oz), whisk 3 tablespoons flour, 3 tablespoons sugar, 2 tablespoons unsweetened cocoa, ¼ teaspoon baking powder, and a pinch of salt until no cocoa lumps remain.

2. 2

   Stir in 3 tablespoons milk, 2 tablespoons neutral oil or melted butter, and ¼ teaspoon vanilla until the batter is smooth and looks like thick chocolate cake batter — scrape the bottom corners so no dry flour hides there.

3. 3

   Press 1 square of semisweet chocolate (about ½ oz) or 1 tablespoon chocolate chips into the center of the batter so it's buried but not touching the bottom.

4. 4

   Microwave on high 45–70 seconds. Start at 45 seconds: the top should look set and cake-like with a glossy, slightly soft spot in the middle. Add 10-second bursts if needed — overcooking kills the lava. Rest 1 minute; the center is molten-hot. Spoon in carefully. You want a soft cake rim with a warm chocolate center that runs when you dig in — not a dry mug cake or a raw liquid batter.