To prepare the stuffing, first wash the lemons, then blanch them and grate them. Grate the insides of the citrus too.
Sift the flour with baking powder and salt and mix well. Leave the butter to soften in advance. Then beat it with the sugar to whiten and add the eggs one by one; you have to set aside 1 yolk.
Combine the egg and powdery mixtures. Knead a soft dough quickly, shape it into a ball and put it in the fridge for about 20 minutes.
Mix the lemons with 4/5 cup (200 g) of sugar (or less) and the starch to prepare the filling. Spread out half of the chilled dough on the bottom and sides of a baking dish. On it, add the filling and cover with the remaining dough.
Smear with the yolk on top (optional) and bake until golden.