In a large saucepan over medium heat, add water, butter, and sugar. Bring to a boil, then add vanilla. Turn off heat, add flour and salt, and stir with a wooden spoon until thickened, about 30 seconds. Let mixture cool for 10 minutes.
During this time, mix cinnamon and sugar and pour in large flat plate.
To cooled mixture, using a hand mixer, beat in eggs one at a time until combined. Transfer mixture to a piping bag fitted with a large open star tip.
In a large flat wide pot over medium heat, add approximately 1" high of oil and heat to 375°. Holding the piping bag a few inches above the oil, carefully pipe churros into 5-6" long ropes. Use kitchen scissors to cut off dough from piping bag.
Fry until golden, 4 to 5 minutes, turning as necessary. Fry 3 to 4 churros at a time and let oil come back to 375° before each batch. Remove churros with a slotted spoon or tongs and immediately roll churros in cinnamon sugar, then place on a cooling rack.
