In a mixing bowl, add the butter, flour, powdered sugar, baking powder, salt, and egg. Mix on medium to high speed until a homogeneous dough forms.
Shape the dough into a disc, wrap it in plastic wrap, and refrigerate for 1 hour.
Preheat the oven to 160° C/320° F, on convection mode.
On a clean work surface, place two sheets of parchment paper, sprinkle them with flour, and roll out the dough between them using a rolling pin. If the dough sticks, sprinkle a bit more flour.
Grease and flour a 25 cm (10 inch) round tart pan with a removable base, place the dough inside, and press it firmly against the bottom and sides of the pan. Use a knife to trim any excess dough.
Prick the entire surface of the bottom with a fork, cover with a sheet of parchment paper, and add rice or beans to cover the bottom. This creates weight to prevent the dough 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 it turns golden brown.