Spray four 5-ounce or 6-ounce ramekins with cooking spray. Sprinkle about 3 teaspoons of brown sugar into each ramekin. Fill each cup with ½ cup of blueberries.
In a bowl whisk the remaining dry ingredients plus the remaining brown sugar until mixed. Add the egg, butter, vanilla and buttermilk and mix. Spoon evenly into ramekins. Place ramekins in air fryer basket.
Air fry at 320°F for about 14 to 15 minutes. Check with a toothpick at 12-13 minutes. If it comes out clean, they’re done.
To Bake In The Oven: Preheat oven to 350F. Bake for 20-25 minutes or until a toothpick inserted near the center comes out clean.
Let cool for 5 minutes. Run a small knife around the edges to loosen, then carefully invert each cake onto a serving plate. If the tops have puffed up, trim them slightly so they sit level before flipping. Serve with light vanilla ice cream or whipped cream, if desired.