Preheat the oven to 200°C/Gas 6.
Place the milk, cold water, salt, sugar into a pan on low heat, add the butter and bring to boil. Turn off the heat then tip in the sifted flour and beat vigorously with a wooden spoon. As soon as the mixture starts to come away from the side of the pan, stop beating and tip onto a plate to cool.

Return the mixture to the pan and gradually beat in one egg at a time, mixing well between each addition, until you have a smooth paste.

Using a piping bag, pipe walnut-sized balls onto a greaseproof baking sheet, well distanced, and bake for 18 minutes or until golden brown. Let it cool completely on a cooling rack before filling.

For the cream, heat up the milk (except for a glass to be used later on), half of the sugar and the vanilla pod - both seeds and pod - in a pot on medium heat.

In an electric mixer or a mixing bowl, beat the egg yolks and the rest of the sugar until they form a fluffy mixture. Set aside. Sift the flour in a separate bowl and set aside.

Once the milk starts to boil, remove the vanilla pod and remove from heat. Gradually beat in the flour while mixing energetically. Add the yolks and sugar mixture and stir well, then add the last glass of milk (heated up) and the peel of half a lemon. Do not include the white part of the peel since it is bitter.

Return to heat and stir well until the cream starts to boil or has thickened enough. Don't forget to remove the lemon peel before serving. Transfer the cream into a bowl and let it cool completely.