In a saucepan, add the butter, granulated sugar, water, and salt.
Bring to a boil on medium-high heat, constantly stirring.
Once boiling, reduce the heat to medium and mix in the flour, using a Danish dough whisk or a wooden spoon.
Mix until you have a smooth dough. (It's best to use a dough whisk or a wooden spoon that is heatproof.)
Once it is a dough, remove it from the heat and let it cool for 5-6 minutes.
Place the dough in a large mixing bowl and add 1 egg at at time, mixing well in between each. This is best done with a handheld mixer.
Add in the vanilla extract.
Place the dough in a piping back with a large star tip such as a Wilton 1M tip.
Refrigerate the dough for at least 30 minutes or overnight.
When ready to make, preheat the air fryer at 360*F for 5 minutes.
Carefully pipe the dough into 4-inch long tubes directly into the air fryer basket. One you are done piping them, use scissors to cut off the dough.
Air Fry at 360*F for 8-9 minutes. If you use a different size piping tip then the times may be altered.
Take them carefully out of the basket.
Brush the melted butter onto each churro then roll them in cinnamon and sugar.
Place on a cooling rack to completely cool off and serve.