Heat the water, butter and sugar to the boil, stirring to dissolve the sugar.
When boiling quickly add the flour and cocoa powder and stir briskly to combine. Keep cooking for roughly a minute or until the mixture comes together and forms a loose ball.
Take off the heat and leave to cool for roughly 10 minutes - you're going to add the eggs next and don't want them to cook.
Add each egg one at a time and stir to incorporate completely before adding the next. You should finish up with a smooth, slightly springy dough.
Place into a piping bag with a large star tip and pipe over the backs of an overturned muffin tin, making sure there are as few gaps as possible. Freeze for at least three hours, or until they've set.
Preheat the groundnut oil to 180°C/360°F. Carefully prise the bowls from the muffin tin and fry each one separately for roughly 2 - 3 minutes, until they have puffed up and cooked through. Drain and dry with kitchen towel.
In a medium bowl mix together the caster sugar with the cocoa powder (sift the cocoa powder first), then roll the warm bowls one at a time in the cocoa sugar mixture.
Break the white chocolate into small pieces and heat the cream up to almost boiling, then pour over and mix together to a smooth ganache.
Pour the ganache into each churro bowl and sprinkle with broken up cookies.