Place the diced butter into a saucepan, add water and a pinch of salt and bring to the boil.
Sieve the flour and baking powder together. As soon as the water and butter mixture boils, remove it from the heat and quickly stir in the sifted flour and baking powder. Beat the mix with a silicon spoon until smooth and it comes away from the sides of the pan in a smooth mass.
Tip the mixture into a bowl and cool for a couple of minutes. Then gradually add the beaten eggs one at a time, beating well until the mixture is smooth, glossy and drops reluctantly from a spoon. Cover the bowl with a clean tea towel and leave the batter to one side to rest for 30 minutes.
Finely chop the dark chocolate and place in a bowl. Pour the double cream into a small saucepan, add the cinnamon stick, condensed milk, butter and vanilla extract, and bring to a simmer.
Stir to combine and then pour over the chopped chocolate and stir again until the mixture is smooth.
Fill a large saucepan no more than one third full with oil. Heat until it reaches 180'C-190'C (or a cube of bread browns in a minute). Fit a large piping bag with a large star-shaped nozzle and fill with the batter mix. Once the oil has reached the correct temperature you can start to cook the churros.
Pipe 2 or 3 finger-length strips of batter directly into the pan cutting off each strip with a pair of scissors.
Cook the churros for about 45 seconds to one minute on each side until golden and crisp. Remove from the pan with a slotted spoon, drain quickly on kitchen paper and sprinkle liberally with demerara sugar.
Serve with thick hot chocolate dipping sauce.
«Do not fry more than 2 or 3 churros in one go or the oil will cool down dramatically and your churros will be heavy and greasy, rather than crisp, golden and light. »