In a mixing bowl, whisk together the all-purpose flour, powdered sugar, and salt until well combined.
Add the cold, cubed butter to the flour mixture. Using a pastry cutter or a fork, cut the butter into the flour until it resembles coarse crumbs. Be careful not to overwork the dough; you want small clumps of butter to remain for a flaky texture.
Crack the large egg into the mixture and add 1 teaspoon of milk. Stir until the dough begins to come together. If the mixture is too dry, add an additional teaspoon of milk as needed.
Turn the dough out onto a lightly floured surface and shape it into a disc. Wrap it in plastic wrap and refrigerate for at least 30 minutes. Chilling the dough helps prevent shrinkage during baking.
Once chilled, remove the dough from the refrigerator. On a floured surface, roll it out to fit your tart pan, about 1/8 inch thick. Carefully transfer it to the pan, pressing it into the edges and trimming any excess.
Preheat your oven to 350°F (175°C). Place a piece of parchment paper over the crust and fill it with pie weights or dried beans. Bake for 15 minutes, then remove the weights and parchment and bake for an additional 10 minutes, or until lightly golden.
Once baked, remove the tart crust from the oven and allow it to cool completely before filling it with your favorite fillings.