Preheat the air fryer: Set it to 320°F (160°C) for about 3 minutes.
A slightly lower temperature helps the cake cook through without scorching the top.
Prep your pan: Lightly grease a 10-ounce ramekin, small 4-inch cake pan, or a silicone muffin cup. Line the bottom with a small circle of parchment if your pan tends to stick.
Mix dry ingredients: In a small bowl, whisk together flour, sugar, baking powder, and a pinch of salt until evenly blended.
Add wet ingredients: Add the egg yolk, milk, oil or melted butter, and vanilla. Whisk just until smooth.
Don’t overmix—stop when you no longer see dry streaks.
Fold in extras: If using chocolate chips, nuts, or berries, gently fold them in. Keep the batter thick but pourable.
Fill the pan: Scrape the batter into the prepared ramekin. Smooth the top with the back of a spoon so it bakes evenly.
Air fry: Place the ramekin in the air fryer basket.
Cook at 320°F (160°C) for 10–12 minutes, until the top springs back lightly and a toothpick comes out with a few moist crumbs.
Rest briefly: Let the cake sit for 3–5 minutes. This helps it finish setting and makes it easier to turn out if you like serving it on a plate.
Top and serve: Dust with powdered sugar, drizzle with a simple glaze, or add a scoop of ice cream. Enjoy warm.