In a medium bowl, whisk together flour, sugar, baking powder, and salt.
In a separate bowl, whisk milk, egg, melted butter, and vanilla until smooth.
Pour wet ingredients into dry. Stir gently with a spatula just until combined — a few lumps are fine. Let batter rest 5 minutes.
Preheat air fryer to 350°F (175°C) for 3 minutes. Grease a 6-inch round cake pan generously with cooking spray.
Pour batter into the prepared pan. Scatter blueberries evenly across the top — don't stir them in.
Air fry at 350°F for 7–8 minutes, until the top is set, edges are golden, and a toothpick inserted in the center comes out clean.
Rest in pan 1 minute, then turn out and slice into wedges. Serve warm with butter, maple syrup, and extra blueberries.