How to Make It
For churros: Pour oil to a depth of 2 inches in a Dutch oven and fit with a deep-fry thermometer; heat to 350°F over medium-high. Combine cinnamon and ½ cup of the sugar in a shallow dish. Set aside.
Stir together water, butter, salt, and remaining 2 tablespoons sugar in a large, heavy-duty saucepan over medium-high. Bring to a boil, stirring, until butter melts. Reduce heat to low, add flour all at once, and cook, stirring constantly, until mixture forms a ball, about 30 seconds. Remove from heat and add eggs, 1 at a time, stirring vigorously until dough is smooth and elastic after each addition.
Spoon mixture into a piping bag fitted with a large star tip. (Or place mixture in a large ziplock plastic freezer bag, and snip 1 corner to make about a 1/2-inch hole.) Working in batches, pipe 4-inch-long strips into hot oil, and fry, turning occasionally, until golden brown, 8 to 10 minutes.
Transfer churros to a paper towel-lined baking sheet to drain, and immediately roll in cinnamon-sugar mixture.
For chocolate sauce: Stir together chocolate, cream, and vanilla in a small microwave-safe bowl. Microwave on high, stirring every 30 seconds, until melted and smooth, about 1 1/2 minutes. Serve warm with churros.