In a bowl, mix caster sugar and cinnamon powder. Set aside.

In a heavy-bottomed pan, bring water, butter, sugar, and salt to a simmer over medium heat.

Reduce heat to low and add flour. Whisk continuously to prevent sticking.

Cook while stirring until the mixture forms a smooth ball, about 8–9 minutes.

Turn off heat and allow the dough to cool for 3–5 minutes.

Add eggs one at a time, whisking well after each addition.

Add vanilla extract and mix until the dough is thick but drops easily. If too stiff, add 1 teaspoon water.

Transfer dough to a double piping bag fitted with a 1M star nozzle.

Heat oil in a heavy pot to 125°C / 257°F.

Pipe churros directly into the oil, cutting into 4-inch lengths.

Fry on medium heat for 4–6 minutes per side until golden brown and fully cooked inside.

Drain on paper towels and immediately coat with cinnamon sugar while hot.

Heat milk and cream on low until just beginning to boil.

Pour over chopped chocolate and let sit for 30 seconds.

Whisk until smooth. If needed, reheat gently for 10–15 seconds, stirring constantly.

Cool slightly and serve with churros.