Combine water, butter, 1 tablespoon sugar, and salt in a medium saucepan over medium-high heat. Bring to a full boil — not just steaming, actually boiling.

Add all the flour at once. Switch to a wooden spoon and stir hard. The dough will look shaggy for about ten seconds — keep stirring until it comes together into a smooth ball and pulls cleanly away from the sides of the pan. Remove from heat.

Let the dough cool in the pan for five minutes. This prevents the eggs from scrambling when you add them.

Add the eggs one at a time, stirring vigorously after each addition until fully incorporated. The dough will look slippery and separated at first — keep stirring until it comes back together smooth. Stir in the vanilla extract if using.

Transfer the dough to a piping bag fitted with a large star tip.

Pour neutral oil about 2 inches deep into a heavy pot and heat to 375°F over medium-high heat. Use a thermometer to confirm the temperature before frying.

Pipe 4 to 6 inch lengths of dough directly into the hot oil, cutting with scissors or a knife. Fry in batches — do not crowd the pot. Fry for 2 to 3 minutes per side until deep golden brown.

Remove churros with a slotted spoon or spider strainer and drain briefly on a paper towel-lined plate.

While the churros are still hot and tacky, roll them immediately in the cinnamon sugar mixture until fully coated. Serve warm.