01 - In a medium saucepan set over medium heat, combine water, unsalted butter, granulated sugar, and salt. Stir and bring to a boil.
02 - Reduce heat to low and immediately add all-purpose flour. Stir vigorously using a wooden spoon until the mixture comes together into a cohesive dough that pulls away from the pan sides, approximately 2 to 3 minutes.
03 - Remove the saucepan from heat. Allow dough to cool for 5 to 7 minutes to prevent eggs from scrambling during the next step.
04 - Stir in vanilla extract. Incorporate large eggs one at a time, mixing thoroughly after each addition until the dough becomes smooth, glossy, and thick.
05 - Transfer dough to a piping bag fitted with a star tip. Pipe 1-inch portions onto a parchment-lined baking tray, spacing evenly.
06 - Place the tray with piped dough in the freezer for 10 minutes to help set the shape.
07 - Preheat air fryer to 375°F. Lightly coat the fryer basket with cooking spray.
08 - Arrange chilled bites in the air fryer basket in a single layer. Cook in batches for 8 to 10 minutes until puffed and golden brown.
09 - While still warm, brush churro bites with melted butter then roll in the cinnamon-sugar mixture until evenly coated.
10 - Serve churro bites warm. Accompany with chocolate sauce or caramel if desired.