Make the Tart Crust:

1. Prepare the dough: In a food processor, combine flour, powdered sugar, and salt. Pulse to mix. Add cold butter cubes and pulse 10-12 times until mixture resembles coarse crumbs with some pea-sized butter pieces remaining. Add egg yolk and vanilla, then pulse until dough just begins to come together. If dough seems too dry, add ice water one tablespoon at a time.
2. Chill the dough: Turn dough out onto a clean surface and gently press into a disk. Wrap tightly in plastic wrap and refrigerate for at least 1 hour or up to 2 days.
3. Roll out the dough: On a lightly floured surface, roll chilled dough into an 11-inch circle, about ⅛-inch thick. Carefully transfer to a 9-inch tart pan with removable bottom, pressing dough into the bottom and up the sides. Trim excess dough by rolling your rolling pin across the top of the pan. Prick the bottom all over with a fork.
4. Chill again: Place the tart shell in the freezer for 15 minutes. Meanwhile, preheat oven to 375°F (190°C).
5. Blind-bake the crust: Line the chilled tart shell with parchment paper and fill with pie weights or dried beans. Bake for 15 minutes, then carefully remove parchment and weights. Bake for an additional 10-12 minutes until the crust is golden brown. Remove from oven and let cool completely.

Make the Orange Filling:

6. Prepare the oranges: Zest 2-3 oranges to get 2 tablespoons of zest (zest before juicing!). Juice enough oranges to get 1 cup of fresh juice. Strain out any pulp or seeds.
7. Cook the filling: In a medium saucepan, whisk together sugar, eggs, egg yolks, and cornstarch until smooth. Add orange juice, orange zest, and a pinch of salt. Whisk to combine thoroughly.
8. Heat and thicken: Place the saucepan over medium heat. Cook, whisking constantly, for 5-7 minutes until the mixture thickens considerably and begins to bubble. It should coat the back of a spoon and leave a clear path when you run your finger through it.
9. Finish the curd: Remove from heat and immediately whisk in the butter pieces until completely melted and incorporated. The filling should be smooth and glossy.
10. Strain for smoothness: Pour the orange curd through a fine-mesh strainer into a clean bowl to remove any cooked egg bits or zest pieces. This ensures an ultra-smooth filling.

Assemble the Tart:

11. Fill the tart: Pour the warm orange filling into the cooled tart shell. Use a spatula to spread it evenly to the edges.
12. Chill and set: Refrigerate the tart for at least 3-4 hours, or until the filling is completely set and firm to the touch. For best results, chill overnight.
13. Serve: Before serving, carefully remove the outer ring of the tart pan. Top with whipped cream, candied orange slices, fresh orange segments, or a dusting of powdered sugar if desired. Slice with a sharp knife, wiping clean between cuts for the cleanest slices.