Prepare Churro Batter: In a pot, combine 1 cup of water, 7 tablespoons of unsalted butter, 1 tablespoon of white sugar, and 1/2 teaspoon of salt. Bring this to a boil.
Cook Flour: Add 1 cup + 2 tablespoons of all-purpose flour to the boiling mixture. Cook for 2 or 3 minutes, or until a film develops on the bottom of the pot.
Add Eggs: Transfer the mixture to a bowl. Work in 3 whole eggs one at a time, ensuring each is fully incorporated before adding the next.
Add Flavors to Batter: Stir in 1 teaspoon of vanilla extract and 1/4 teaspoon of ground cinnamon into the batter.
Make Cinnamon Sugar: Combine 1 cup of sugar with 1 tablespoon of cinnamon. Set aside.
Prepare Chocolate Sauce: In a pot on medium heat, add 3.53 ounces (100 g) of heavy cream, 1 tablespoon of light corn syrup, 1/2 teaspoon of vanilla extract, and a pinch of kosher salt. Once it comes to a boil, pour it over 1.9 ounces (55 g) of dark chocolate and stir to combine.
Fry Churros: Pipe the churro batter into hot oil at 375° F, cutting with scissors to desired length. Fry for about 2 minutes on each side, then drain on paper towels.
Coat with Cinnamon Sugar: Toss the fried churros in the cinnamon sugar mixture while they are still hot.
Serve: Enjoy the churros with the chocolate sauce.