Prepare the Dough:

In a medium saucepan, bring the water, butter, sugar, and salt to a simmer over medium heat. Once the butter has melted and the mixture is simmering, remove from heat and add the flour all at once. Stir vigorously until the dough forms a ball.

Add Eggs and Vanilla:

Allow the dough to cool for a couple of minutes. Then, add the eggs, one at a time, mixing well after each addition. Stir in the vanilla extract.

Heat the Oil:

Heat vegetable oil in a deep frying pan or pot to 375°F (190°C).

Pipe the Churros:

Transfer the dough to a piping bag fitted with a star tip. Once the oil is heated, pipe 4–5-inch churros directly into the hot oil, cutting them with scissors. Fry 3–4 churros at a time for about 2–3 minutes on each side, or until golden brown and crispy.

Coat the Churros:

In a shallow bowl, combine the sugar and cinnamon. As soon as the churros are done frying, remove them from the oil and coat them in the cinnamon sugar mixture.

Optional Filling:

If you’re filling the churros, let them cool slightly and then pipe dulce de leche (or chocolate) into the center of each churro.

Serve:

Serve the churros warm, with extra dulce de leche for dipping if desired.