In a medium saucepan, combine the water, butter, sugar, and salt. Heat over medium-high heat until the butter is melted and the mixture is boiling. Immediately remove from the heat.

Add all the flour at once and stir vigorously with a wooden spoon or silicone spatula until all the flour is incorporated, about 1 minute.

Return the pan to medium-low heat and cook, stirring constantly, for 1 to 2 more minutes to cook off any excess moisture. (The mixture should look like very thick mashed potatoes and come away from the sides and bottom of the pot cleanly.) Transfer the mixture into the large bowl of a stand mixer fitted with a paddle attachment (or you can use a hand mixer right in the pot!).

Mix on medium speed for about 3 minutes, until the mixture has cooled slightly. Add the eggs one at a time, mixing until thoroughly combined before adding the next. Add the vanilla. Scrape the sides and the bottom of the bowl as needed. The dough should be smooth, glossy, and thick, and should hold its shape for a few seconds when swiped with a spatula before very slowly falling back into the dough.

Place the mixture in a piping bag fitted with a large, closed star tip (Wilton 1M.) Pipe churros that are about 4 inches long, and about ¾-inch wide onto a small, parchment-lined baking sheet. (Use a paring knife to cut through the dough at the tip when you are finished piping a churro, for a clean edge.) Place in the freezer for 30 minutes.

Place the chilled churros in an air fryer basket, leaving about 1 inch of space between each. Air fry at 375°F for 8 minutes. Flip once, then air fry at 325°F for another 8 minutes, until golden brown, and dry in the center.

Meanwhile, stir to combine the sugar and cinnamon in a shallow, wide bowl. While the churros are still hot, toss them in the cinnamon sugar. If sugar isn’t sticking, spray them lightly with vegetable spray before dredging.