Grease a large baking sheet. Pour the measurement water into a medium saucepan, add the butter and salt and heat until the butter has melted. Bring to the boil, then take off the heat and stir in the flour. Put the pan back on the heat and cook briefly, stirring until the mixture makes a smooth ball. Leave to cool.
Beat the eggs and vanilla extract into the paste gradually until smooth. Spoon the choux pastry into a large piping bag fitted with a 1.5 cm (¾ inch) plain nozzle, and pipe 20 balls onto the baking sheet, leaving space in between.
Bake in a preheated oven, 200°C (400°F), Gas Mark 6, for 15 minutes until well risen. Make a slit in the side of each ball for the steam to escape, then return to the turned-off oven for 5 minutes. Leave to cool.
Make the sauce by heating the chocolate, milk and sugar in a saucepan and stirring until smooth. Take off the heat and mix in the brandy. Whip the cream until it forms soft peaks, then fold in the ginger. Enlarge the slit in each profiterole and spoon in the ginger cream. Pile into serving dishes and drizzle with the reheated sauce.