Preheat your oven to 190°C (375°F). Line a large baking sheet with parchment paper.

In a medium saucepan, combine the butter, granulated sugar, and water. Place over medium-low heat. Stir occasionally until the butter has completely melted and the mixture comes to a full, rolling boil.

As soon as the mixture boils, remove the pan from the heat. Immediately add all of the sifted cake flour at once.

Quickly stir with a wooden spoon or stiff silicone spatula until the flour is fully incorporated and a smooth dough forms, pulling away from the sides of the pan into a ball. This should take about a minute.

Let the dough cool for 5-7 minutes, until it's warm but not hot to the touch (you don't want to cook the eggs).

Add the vanilla extract to the warm dough.

Then, begin adding the lightly beaten eggs. Add them in 3-4 separate additions, stirring vigorously with your spatula after each addition until the egg is fully absorbed before adding the next.

The dough will initially look slippery and separate but will come together with mixing. After all the eggs are added, you should have a very smooth, glossy, and thick paste that holds its shape but slowly slides off the spatula.

Fit a large piping bag with a large open star tip (like a 1M or 8B). Spoon the churro dough into the bag.

Pipe 5-8cm (2-3 inch) long straight lines onto the prepared baking sheet, leaving about 2cm (¾ inch) of space between them as they will expand slightly. You can also pipe them into classic loop shapes if you prefer.

Bake on the middle rack for 20-25 minutes, or until the churros are puffed, firm to the touch, and beautifully golden brown. Do not open the oven door during the first 15 minutes of baking.

While the churros bake, mix the powdered sugar and cinnamon powder together in a wide, shallow bowl or plate.

As soon as the churros are out of the oven and cool enough to handle (but still warm), roll each one generously in the cinnamon-sugar mixture until fully coated.

Serve immediately while still warm and crisp, with chocolate sauce on the side for dipping.