In a medium saucepan, combine 1 cup water, 1/3 cup + 1 tbsp unsalted butter, 1 tsp salt, and 2 tbsp sugar. Bring to a rolling boil, then reduce heat to medium-low. Gradually add in 1 cup plain flour while stirring continuously until the dough pulls away from the sides of the pan and forms a smooth ball (about 2-3 minutes). Turn off heat and remove the pan from the stove.

Transfer the hot dough into a large mixing bowl and let cool for 4-5 minutes. Once slightly cooled, add in 1 large egg and 1 tsp vanilla extract. Use an electric hand mixer to beat until you have a smooth, glossy mixture that’s pipeable (about 1-2 minutes).

Transfer the churro dough into a piping bag. Preheat your air fryer to 375°F (190°C) and spray the basket with nonstick cooking spray.

Carefully pipe bite-sized churros (about 1.5-2 inches long) into the air fryer basket, leaving space between each. Lightly brush tops with melted butter, then cook for 10-12 minutes until golden brown and puffed. Work in 2-3 batches if necessary.

While warm, transfer churros into a shallow bowl with 1 cup white sugar mixed with 1 tbsp cinnamon powder. Toss gently to coat.