In a saucepan, bring the water, butter, sugar, and salt to a boil. Lower the heat and add the flour all at once. Stir vigorously with a wooden spoon until the dough forms a smooth ball and pulls away from the sides of the pot. Remove from the heat and let it cool for 5–10 minutes before adding the eggs.

Add the eggs one at a time, mixing thoroughly after each addition. The dough should become smooth, shiny, and pipeable.

Transfer the dough to a piping bag fitted with a star-shaped tip. Pipe small 2–3 cm pieces directly into hot oil (170°C / 340°F). Fry in batches for 1–2 minutes per side until golden brown and crisp. Remove and place on paper towels to drain excess oil.

In a large bowl, mix sugar and cinnamon. While still warm, toss the churro bites in the mixture until they’re evenly coated.

In a saucepan, combine sugar and cornstarch. Gradually whisk in the milk until smooth and lump-free. Heat over medium heat, stirring constantly, until the mixture starts to thicken. Remove from the heat, then stir in butter, salt, and dark chocolate until fully melted and glossy. If the sauce becomes too thick, add a splash of milk until you reach your desired consistency.