Pour the flour, almond powder, sugar and salt into a bowl and mix. Add the butter cut it into small pieces, and mix to incorporate the butter into the flour.

Form a fountain and pour in the beaten egg. Gather the dough with your fingers until it is homogeneous without overworking it. Add a little water (the equivalent of half an eggshell) if necessary.

Crush the dough with the palm of your hand (milling) to incorporate all the elements. Form the dough into a smooth, soft ball. Set aside in a cool place for at least two hours.

Cut the lemons into 2 mm slices. Blanch the lemon slices for 2 or 3 minutes, then drain them. Mix 15o ml of water, the lemon juice with the caster sugar and bring to a boil in a pan. Add the lemon slices. Cook over low heat for about 30 minutes until they become translucent and melting. Set aside to cool.

Roll out the pastry to a thickness of 2/3 mm and fill a 26 cm diameter and 2 cm high tart mould (or several small tart moulds) with butter.

Prick the pastry with a fork. Set aside in a cool place while the oven heats to 350° F (180° C).

Place a sheet of baking paper with peas or beans on top of the pastry. Pre-bake for 15 minutes. Remove the paper and peas and continue baking at 320° F (160° C ) for 15-20 minutes (depending on the oven and the size of the pies). Remove from the pie tin and allow to cool on a wire rack.

Mix the eggs with the sugar, cornflour and lemon zest, then whisk in the milk.

Add the lemon juice, heat in a saucepan over medium heat and bring to a boil, stirring. Continue over moderate heat until thickened, stirring constantly. Remove from the heat and whisk in the butter, cut into cubes.

Set aside for a moment before garnishing the tart shell.

Pour the lemon cream over the tart base, leave to set in a cool place for at least two hours, and then arrange the slices of preserved lemon.