1.For the churro dough: Heat 2 inches oil to 350 degrees F in a wide 3 1/2 to 4-quart heavy pot over high heat. In a medium saucepan over medium-high heat, combine 1 cup water and the cinnamon stick and bring to a boil. Discard the cinnamon stick. Add the butter, sugar and salt and stir until the sugar dissolves and the butter melts.

2.Turn off the heat. Using a wooden spoon, quickly stir in the flour until it is well combined and a shiny dough forms. Return the pan to medium-heat and cook the dough, stirring, until it starts to pull away from the sides of pan, about 2 minutes.

3.Transfer the dough to a medium bowl and let cool, about 5 minutes. Beat in the eggs, 1 at a time, stirring vigorously after each addition, until the egg is completely incorporated (the dough will be sticky.)

Pull of 1-inch pieces of dough and stuff them with the chocolate chips. I used about 6-7 chips and was able to cover them completely in dough. It's important that the chocolate chips be completely covered or they will ooze out as soon as they touch the grease. Fry the churro donuts, 6 at a time, turning occasionally, until golden brown. Drain on paper towels.

For the cinnamon sugar topping: Combine the sugar and cinnamon in a shallow bowl.

Roll the churro donuts in cinnamon-sugar while they are still hot. It's best to eat them immediately while the chocolate stuffing is still nice and warm.