Heat the butter, salt, garlic and 90ml water in a large pan until it comes to the boil. In a bowl, mix the flour, cayenne and white pepper, then, 1 tbsp at a time, add the mixture to the pan, stirring constantly over a low heat. When the choux dough is smooth and coming away cleanly from the sides of the pan, remove from the heat and leave to cool for 10 minutes. Tip the dough into a large, wide bowl and, 1 at a time, beat in the eggs, only adding more egg once the previous one is fully incorporated. Fold 1/2 the parmesan through the dough and put into a piping bag fitted with a 1cm nozzle.