For the chocolate profiteroles, increase the oven to 200 ºC and lightly grease a large baking tray with butter.
Put the butter, sugar and water into a medium saucepan and place over a low heat to melt the butter. Increase the heat and then quickly add all of the flour and salt.
Using a wooden spoon, beat the mixture until it starts to come away from the sides of the pan. Beat in the eggs, one at a time. (The mixture should be shiny and smooth with a soft dropping consistency.)
Dip a teaspoon into some warm water and lift out a spoonful of the profiterole mixture. Rub the top with a wet finger to remove any bumps and place onto the prepared baking tray. Repeat until all of the mixture has been used up.
Place the tray into the oven and bake for 25-30 minutes, or until golden-brown. Remove from the oven and prick the base of each profiterole with a skewer. Place onto the baking tray with the hole facing upwards and return to the oven for five minutes. Remove the profiteroles from the oven and set aside to cool.
To make the filling, whisk the cream in a bowl until soft peaks form when the whisk is removed. Stir in the vanilla seeds and whisk until well combined. Spoon the vanilla cream into a piping bag fitted with a 0.5cm/¼in plain nozzle.