In a large bowl, combine the flour, salt, and butter. Wearing disposable gloves, start rubbing the butter into the flour between your fingers until the mixture resembles breadcrumbs.
Add the egg and knead until a smooth dough forms.
Shape the dough into a disc, wrap it in cling film, and refrigerate for 1 hour.
Preheat the oven to 160° C/320° F, on convection mode.
Place two sheets of parchment paper on your work surface, sprinkle with a little flour, and roll out the dough between them with a rolling pin. If the dough sticks, sprinkle with a bit more flour.
Butter and flour a 25 cm (10 inch) round tart pan with a removable base. Press the dough into the pan, making sure it adheres to the bottom and sides. Trim any excess dough with a knife.
Prick the bottom of the pastry all over with a fork, cover with a sheet of parchment paper, and fill it with rice or beans to weigh it down and prevent the pastry from puffing up while baking.
Bake in the oven for 30 minutes, then remove the parchment paper and beans. Brush the tart with the egg wash and bake again until golden brown.