Fill a large pan 2 inches deep with oil over medium heat. I like to use my Dutch oven. Heat oil to 365-375°F. While the oil is heating up, continue following the next steps.
Line a large plate with paper towels and set aside. Make the cinnamon sugar topping by combining the sugar and ground cinnamon in a shallow bowl. Set aside.
In a separate saucepan over medium heat, add water, butter, sugar, salt, and vanilla extract. Stir frequently until butter is melted and mixture comes to a boil.
Once boiling, reduce heat to low and add flour. Stir until a dough ball forms. Remove from heat and allow to cool for 15 minutes.
After cooling, add one egg and stir with a wooden spatula until well until combined. This will be difficult at first and the mixture won't seem to come together, but use a spatula or wooden spoon to continue to stir until the egg is combined. (To make this easier, you can use a stand mixer if you have one.)
Once the egg is fully mixed in, add the second egg and repeat. This will be even tougher to mix in than the first one, but keep going and the mixture will come together to form a dough.
Transfer the dough to a large sturdy piping bag fitted with a large star tip (I used a Wilton #6b).
Once oil has reached 365-375°F, carefully pipe a 4-5 inch line of dough into your oil. Quickly cut the dough from the tip using scissors.
Fry for about 3 minutes until golden brown, then transfer to the plate lined with paper towels to drain off any excess oil.
Roll the churros through cinnamon sugar topping until coated on all sides and transfer to a plate for serving.
Serve immediately with chocolate dipping sauce if desired.
For the chocolate dipping sauce
Add the chocolate chips in a medium bowl. Set aside.
Add the heavy cream, cinnamon, and salt to a small saucepan over medium-high heat. Give it a stir to mix everything together and heat it up until almost boiling (don’t let it boil!).
Pour the hot cream mixture over the chocolate chips. Stir everything together until the chocolate has melted. Serve immediately.
Notes
Measure the temperature of the oil using a candy/deep fry thermometer. This will help ensure that the oil is at the right temperature so you don't accidentally burn the outside or undercook the middle of the churros.
Use a large star tip like the Wilton #6b or an Ateco 845. It will give you thick and fluffy churros with defined edges.
Make sure to use a very sturdy piping bag. The dough is very thick and if the piping bag isn’t strong enough, it may burst open at the seams when piping. Grab a professional-grade piping bag like this or this.
I recommend frying only 3 churros at a time so that the oil doesn’t drop in temperature too much.