Heat the cream in a pan, remove the pan from the heat. Add the chocolate and stir to melt.
Choux pastry dough
Bring the water, butter and salt to the boil, reduce the heat. Add all of the flour and cocoa powder at once, stir with a risotto spoon for approx. 1 1/2 mins. until a smooth dough is formed which separates from the base of the pan. Remove the pan from the heat.
Gradually stir in the eggs. The mixture should be soft but not runny. Spoon the mixture into a piping bag with a serrated nozzle (approx. 10 mm in diameter)
Fill a pot to 1/3 with oil and heat it to approx. 160°C. Pipe the dough (approx. 10 cm long) into the hot oil in batches, cut with scissors, deep-fry for approx. 6 mins. Remove and drain on paper towels. Mix the sugar and vanilla, toss the churros in the sugar.