Whisk together granulated sugar and ground cinnamon in a shallow dish; set aside.

In a large pot, pour about 1.5 inches of vegetable oil and heat it to 360°F.

In a saucepan, bring water, unsalted butter, granulated sugar, and salt to a boil; add the all-purpose flour and stir until smooth.

Transfer the dough to a bowl and allow it to cool for about 5 minutes.

Mix in vanilla extract and the large egg using an electric mixer until smooth.

Fit a piping bag with a star tip and fill it with the churro dough; pipe 6-inch lengths into the hot oil.

Fry the churros for about 2 minutes on each side until golden brown and crisp.

Once fried, roll the churros in the sugar-cinnamon mixture while still warm and serve immediately.