Preheat oven to 170°C and lightly grease a non-stick baking tray. Sift the flour into a mixing bowl. Bring the water and diced butter to the boil in a large saucepan until the butter has melted.

Tip in the flour in a steady stream, whisking all the time until the mixture clings to the whisk. Swap the whisk for a wooden spoon and beat well for 2-3 minutes until it comes away from the side of the pan easily and drops easily off the spoon.

Take it off the stove. Beat in the eggs one at a time. To do this, use either a wooden spoon or electric whisk. You are aiming for a mixture that is smooth and glossy.

Using a dessert spoon or piping bag with 1cm nozzle, place 18 equal sized balls of pastry on the baking tray lined with greaseproof paper. Bake for 18-20 minutes until golden and puffed. Once cooked, remove from the oven and leave to cool.

The make the Chantilly cream, add the cream, vanilla extract and sugar to a large bowl. Whisk them to form soft peaks using an electric whisk or hand whisk. Create a slit in each profiterole with the nozzle, then pipe the cream filling into each profiterole.

For the sauce, break up the chocolate and add to a heatproof bowl, over a pan of simmering water (without letting the bowl touch the water) and stir until melted. Serve the profiteroles and drizzle over the melted chocolate.