Choose the right mug. Use a microwave-safe mug that holds at least 12 ounces. A wider mug cooks more evenly than a tall, narrow one.

Whisk the egg first. Crack the egg into the mug and whisk with a fork until well blended. This prevents streaks of egg white in the finished cake.

Add Nutella. Spoon in the Nutella and mix until the batter is smooth and uniform. If the Nutella is stiff, microwave it in the jar for 10 seconds first to loosen it.

Stir in flour. Add the flour and a pinch of salt if using. Mix just until you no longer see dry streaks. Don’t overmix—gentle is best.

Customize (optional). Fold in a few chocolate chips or nuts for extra richness and crunch.

Microwave in short bursts. Cook on high for 45–60 seconds, then check. The top should look set around the edges with a slightly soft center. If needed, continue in 10–15 second bursts until done. Most microwaves finish this cake between 60–90 seconds.

Rest briefly. Let the mug cake sit for 1–2 minutes. It continues to set and becomes easier to eat without burning your tongue.

Top and enjoy. Add a scoop of ice cream, a drizzle of cream, or fresh berries. Eat warm with a spoon.