Combine butter, sugar, vanilla, salt, and water in a saucepan. Simmer until butter is fully melted.
Take off the heat and stir in flour dough comes into a ball.
Add egg and beat until smooth.
Transfer the dough to a piping bag with a star-shaped tip.
Pipe 3-inch pieces onto a baking sheet lined with parchment.
Chill for an hour.
Line the air fryer basket with parchment.
Transfer the churros into the basket and cook for 10 minutes at 375F.
Meanwhile, stir together sugar and cinnamon in a bowl.
Take churros out of the air fryer and toss in the cinnamon sugar until well coated.
Serve with chocolate syrup on the side.