Preheat the oven to 210°C.
Cut the butter into small pieces.
Place the water, 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 to 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 third egg.
Place the mixture into a piping bag and pipe small profiteroles on to a baking tray. Bake for 10 to 15 minutes.
Zest and juice the lemons.
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 add the lemon juice and zest. Return the pan to the heat. 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 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 profiterole and fill with the crème pâtissière.
Zest the two lemons. Slightly warm the fondant icing and stir the zest. Dip the top side of the profiterole into the lemon icing and allow to set.
«To make eclairs use the same choux pastry mix and pipe 5 cm by 1.5 cm lengths. To boost the flavour add bit of limoncello into the pastry cream.»