Combine the butter, water, sugar, and milk in a medium saucepan. Bring to a boil over medium heat while stirring frequently.
Add flour and continue to mix thoroughly. Remove from the heat and continue to stir until the mixture comes together into a smooth ball.
When the dough reaches the smooth ball stage, transfer it into a large mixing bowl and let it cool for a few minutes.
Add eggs one at a time into the dough mixture, and mix until smooth. I'm using a electric mixer for this. Let the mixture cool for a while.
Preheat the air fryer to 400F.
Place the dough into a piping bag with an open star decorating tip attached.
Pipe the dough onto a parchment paper, at about 3-4 inches each. Alternatively, you may pipe the dough directly into the air fryer basket if you prefer. Spray some oil onto the air fryer basket, and transfer 8 to 10 churros dough into it. Ensure that you leave enough space in between each churro. Spray some oil onto the churros. Cook the churros in the preheated air fryer for about 6-8 minutes until they are golden brown. In a small bowl, mix together the cinnamon and sugar. When the churros are done, add them to the cinnamon sugar immediate and rol them until they are coated.
Allow the churros to cool on a wire rack for a few minutes before serving with any of your favorite chocolate or caramel sauces.