Preheat oven to 180 C / Gas 4. Lightly grease and flour a springform tart tin.
For the tart base:
In a food processor bowl, add sifted flour with cubed butter and eggs. Pulse until a soft pastry ball is formed and easily separates from the walls of the bowl.
Roll out the pastry on a lightly floured work surface and cover base and sides of tin. Prick with fork.
Bake in preheated oven for 15 to 20 minutes, or until slightly golden. Remove and let cool.
For the filling:
In the meantime, add water and 25g (half of the butter) in a small pan over medium heat and bring to the boil.
In a separate bowl, mix lemon juice, lemon zest, caster sugar, cornflour and egg yolks.
Once water reaches boiling point, reduce heat to low and add the lemon mixture to the pan. Whisk vigorously and non-stop until cream thickens. Once small bubbles appear on the surface, remove from heat and let it cool down for a little bit.
While still warm, add the rest of the butter (25g) and mix well. Pour lemon cream on tart base and chill in the fridge. When serving, decorate with thin lemon slices and Chantilly cream.
For a smooth looking cream, you can strain the cream while cooling after cooking to remove lemon zest.