Place water, butter, sugar, and salt into a medium saucepan. Bring to a boil.
Add flour and mix vigorously until dough balls up, and everything is well blended. Remove from heat.
Place dough into the bowl of a stand mixer fitted with a paddle attachment. Mix on low until steam disappears.
Add egg while the machine is on, turn speed up to medium, and mix until incorporated.
Scoop dough into a piping bag fitted with a star piping tip. (I used a Wilton 2D tip. Make sure the tip is slightly rounded -- helps prevent churros from splitting.) Combine cinnamon and sugar on a large plate and set aside.
Heat oil in a large frying pan or stock pot. To test the oil for frying, drop a tiny piece of dough into the oil. Once it browns, you are ready to pipe the churros in.
Pipe the dough directly into the hot oil to desired length and cut with a fork or scissors. Do not pipe too many churros at once. (So they cook evenly.) Straighten and turn churros with a fork frequently. (Helps prevent splitting.) Cook about 2 minutes or until desired color of brown/doneness. (If they brown too fast, the oil is too hot, if they take a long time to brown, the oil is too cold. Aim for 350-375 degrees Fahrenheit.)
Remove churros and place on a paper towel to absorb excess oil. While still warm, roll churros in cinnamon-sugar mixture. Serve with dulce de leche or chocolate sauce, if desired.
* Can mix completely by hand. Allow dough to cool slightly before adding the egg, so it doesn't scramble. Stir vigorously once adding the egg, until it binds together.
* Recipe lightly altered from Happy Foods Tube