Put a saucepan over medium heat. Add the Water (1 cup), Butter (35 gram), Salt (1/2 teaspoon), and Granulated Sugar (1 tablespoon). Let the water come to a boil. Add the All-Purpose Flour (1 cup) and turn the heat to low. Whisk everything together.
Transfer the batter to a bowl. Beat with a wooden spoon to spread it out, then add the Large Egg (3) one at a time and mixing after each. Add in the Ground Cinnamon (1/2 teaspoon).
Heat a pan with Frying Oil (to taste). Fill a piping bag with the batter, then start piping 5-inch strips of batter into the hot oil. Fry for about 3-4 minutes. Make sure not to over crowd the pan. Drain on a paper towel.
Mix together the Granulated Sugar (1/2 cup) and Ground Cinnamon (1 teaspoon), then lay it in a dish. Rub each of the churros in the cinnamon sugar.