In a medium saucepan, combine water, unsalted butter, salt, and sugar over medium heat. Bring to a gentle boil, stirring until the butter melts.

Gradually add in the plain flour, stirring vigorously until a smooth dough forms. Remove from heat and let cool for about 10 minutes.

After cooling, add the egg and vanilla extract and stir until fully incorporated to create a glossy dough.

Preheat the air fryer to 375°F (190°C) and line the basket with non-stick cooking spray.

Transfer dough to a piping bag and pipe small portions into the air fryer basket, leaving space between them.

Lightly brush or spray churros with butter and air fry for 10-12 minutes, until golden brown.

Prepare cinnamon-sugar coating in a shallow bowl by mixing white sugar and cinnamon powder.

Toss warm churros in the cinnamon-sugar mixture ensuring they're thoroughly coated.

Serve warm with sauces like chocolate or vanilla ice cream.