1Line a rimmed baking sheet with parchment paper. Pat the hot dogs very dry with paper towels, then push a skewer into one end of each, about two-thirds of the way through. Dry hot dogs are what let the batter cling.
2Whisk the cornmeal, flour, sugar, baking powder and salt in a medium bowl. In a small bowl, whisk the milk, egg and melted butter, then pour it into the dry ingredients and stir just until no dry streaks remain. The batter should be thick, like soft pancake batter. If it runs off a spoon, stir in a tablespoon of flour.
3Scrape the batter into a tall glass, filling it nearly to the top so you can dunk a whole hot dog. Spread a spoonful of flour on a plate and roll each hot dog in it, then tap off the extra.
4Dunk one hot dog straight down into the glass, twist as you lift it out so the batter coats evenly, and let the excess drip off for a second. Lay it on the parchment-lined sheet. Repeat with the rest.
5Slide the sheet into the freezer for 15 minutes so the batter firms up. Meanwhile, heat the air fryer to 370°F for 3 minutes.
6Spray the air fryer basket well with cooking spray. Lift the chilled corn dogs onto the basket in a single layer with a little space between them, working in two batches if your basket is small. Lightly spray the tops.
7Air fry for 6 minutes, carefully turn each corn dog over, spray any pale spots, and cook 4 to 6 minutes more, until deep golden and the batter is set all the way through.
8Rest the corn dogs for 2 minutes, since the centers are very hot. Serve with ketchup and mustard for dipping.