In a medium saucepan, combine 1 cup of water, 1/2 cup of unsalted butter, 1/4 teaspoon of salt, and 1/4 cup of sugar. Heat over medium-high until it reaches a boil, then reduce to low. Gradually stir in 1 cup of plain flour until a thick, cohesive dough forms. Allow to cool for about 4-5 minutes.

Add in one egg and 1 teaspoon of vanilla essence to the cooled dough. Mix until smooth and well-combined, achieving a thick, pipeable consistency.

Transfer the dough into a piping bag fitted with a large star tip. Preheat the air fryer to 375°F (190°C) while spraying the basket with nonstick cooking spray. Pipe long strips of dough into bite-sized pieces, avoiding overcrowding.

Brush the churro bites lightly with melted butter and air fry them for 10-12 minutes, checking halfway through. They should be golden brown and puffed up.

Mix 1/2 cup of white sugar with 1 tablespoon of cinnamon in a shallow bowl. Toss the warm churro bites in this mixture to coat thoroughly and serve immediately.