For the shortcrust pastry: Cream the softened butter with the sugar, vanilla seeds scraped from the bean, grated lemon zest, and salt. Gradually add the egg and egg yolk, mixing well. Add the flour a little at a time, mixing until a smooth dough forms. Chill in the refrigerator for at least 30 minutes.

For the pastry cream: Bring the milk to a boil with the split vanilla bean and lemon peel, then strain. In a mixing bowl, whisk the egg yolks with the sugar, then add the sifted flour and finally the hot milk. Cook the mixture in a double boiler until thickened. Sprinkle a little granulated sugar on top and let cool completely.

When all the components are ready, remove the pastry from the fridge and roll it out on a sheet of parchment paper. Place it in a tart pan, prick the bottom with a fork, and fill with the pastry cream. Arrange the plums in a circular pattern on top and sprinkle with granulated sugar.

Bake in a preheated conventional oven at 350°F (180°C) for 35-40 minutes or until golden brown.

Let cool completely. Dust with powdered sugar and serve.