Preheat the oven to 210°C.
Cut the butter into small pieces.
Place the water, sugar, salt and butter in a saucepan and bring to the boil. Once boiling, remove from the heat and mix in the sifted flour. Return to the heat and mix until the mixture no longer sticks to the bottom of the pan. Transfer into a food processor and beat in the eggs one by one. The mixture should be shiny and smooth and have a dropping consistency. You may not need to add the whole of the last egg.
Place the mixture into a piping bag and pipe small choux buns on to a baking tray. Transfer to the oven and bake for 15 minutes until puffed and golden brown. Reduce the oven temperature to 160'C and cook for another 10 minutes to dry the choux buns. You will need at least 100 choux buns to create a small croquembouche.
Split the vanilla pod and scrape out the seeds. Boil the milk with the vanilla pod.
Break the eggs into a bowl and add the sugar. Whisk energetically for one minute before adding the flour. Next, add the hot milk, mix again and then return to the pan. Bring back to the boil and cook for 3 minutes whisking continuously.
Transfer the crème pâtissière onto a tray, cover with cling film to prevent it from drying and set aside in the fridge.
Once the crème pâtissière is cool, whisk the double cream until you have it has the texture of Chantilly cream and then fold into the cold crème pâtissière. Fill a piping bag with this mixture.
Pierce a small hole in the base of each choux bun and fill with the crème pâtissière.
Make the caramel by dissolving the sugar in a pan with the water and heating to a dark caramel.
Remove from the heat and pour into a steel bowl to prevent the caramel from becoming too dark. Allow to cool for 5 minutes.
Dip the filled choux buns into the caramel and create a cone shape, sticking each choux bun to the previous one.
If the caramel becomes too cold, return it to the heat until it liquifies.
«To prevent burns when dipping into the caramel have a bowl of iced water to hand. If you get hot caramel on your hands dip them immediately into the iced water and peel the caramel off.»