In a mixing bowl, combine the flour and sugar for the crust. Cut in the cold butter with a pastry cutter or your fingertips until the mixture resembles coarse crumbs.
Add the egg yolk and ice-cold water gradually, mixing gently until the dough begins to come together. Knead briefly to form a smooth ball, then flatten into a disk and wrap in plastic. Chill in the refrigerator for 30 minutes.
Preheat your oven to 375°F (190°C). On a lightly floured surface, roll out the chilled dough into a 12-inch circle. Transfer it to a tart pan, pressing it into the edges and trimming excess overhang. Prick the bottom with a fork.
Bake the crust for about 15 minutes or until lightly golden. Remove from the oven and let it cool slightly as you prepare the filling.
While the crust cools, peel the oranges and segment them, removing any pith. Reserve a few slices for garnish if desired.
In a saucepan, whisk together sugar, eggs, orange juice, orange zest, and a tablespoon of flour. Place over medium heat and cook, stirring constantly, until the mixture thickens and reaches a gentle simmer.
Remove the custard from heat and strain it through a sieve into a bowl to remove any lumps or cooked egg bits. Let it cool slightly.
Pour the warm orange custard into the baked tart crust, spreading evenly with a spatula. Arrange orange segments on top for a fresh, colorful finish.
Chill the tart in the refrigerator for at least 2 hours to set the custard and develop flavors.
Just before serving, optionally dust with additional orange zest or powdered sugar for presentation. Slice and enjoy the vibrant, citrusy tart.
