In a saucepan over medium-high heat, add butter, brown sugar, salt, and water, and bring to a boil.
As soon as the butter has fully melted and the mixture begins to boil, take the saucepan off the heat and add the flour. Beat with a wooden spoon until the dough comes together to form a ball that doesn’t stick to the sides of the pan anymore. Let the mixture cool for 5 minutes and then slowly add the eggs, one at a time, making sure to beat each egg into the mixture thoroughly. Add the vanilla and beat a final time, then transfer it to a piping bag with a star nozzle.
Turn a muffin tin upside down and spray with cooking spray. Pipe the dough around the inverted cups in spirals to form bowls. Immediately transfer the tray to the freezer and freeze until solid (at least 3 hours or overnight if you can).
When ready to cook, heat the oil in a deep saucepan until it reaches 175˚C. Remove the muffin tin from the freezer and release the churro bowls. Return any extras to the freezer.
Fry them in batches, until nicely browned, they shouldn’t need any more than 3 minutes.
Once the churro bowls are cooked and golden transfer them to a paper towel-lined plate. Dab off any excess oil then roll them in cinnamon sugar.
To make the chocolate cream, put the chocolate in a medium bowl. Bring the cream to a simmer and pour over the chocolate. Let stand for 30 seconds, then stir well until all the chocolate has melted. Let cool. Taste and add a pinch of salt. Cover and refrigerate for at least 4 hours, or until completely chilled. To serve, whip the cream with an electric mixer until it lightens and holds a shape (but be careful not to over whip or the cream won’t be smooth!). Use immediately or refrigerate until needed.
Match the churro shells into pairs, and square off the bottom side of the bottom half of each pair with a sharp knife, taking care not to puncture the churro. Fill the insides of the shells with chocolate cream, place a teaspoon of salted caramel in each centre and sprinkle in about 2 teaspoons of the hazelnuts per churro cup.
Place the bottom halves on a serving plate and top with it’s churro pair. Serve immediately.