In a large bowl, whisk together the flour and salt. Add the cold, cubed butter and cut it into the flour using a pastry blender, two knives, or your fingertips until the mixture resembles coarse meal with some pea-sized pieces of butter remaining.

Gradually add the ice water, 1 tablespoon at a time, mixing lightly with a fork until the dough just comes together. Be careful not to overmix.

Gather the dough into a disk, wrap tightly in plastic wrap, and chill in the refrigerator for at least 30 minutes, or up to 2 days.

On a lightly floured surface, roll out the chilled dough into a 12-inch circle. Carefully transfer the dough to a 9-inch tart pan with a removable bottom. Press it gently into the bottom and up the sides. Trim any excess dough, leaving a 1/2-inch overhang, then fold the overhang in and press against the rim of the pan to create a sturdy edge. Prick the bottom of the crust all over with a fork.

Chill the prepared tart shell for another 15 minutes. Preheat oven to 375°F (190°C).

Line the chilled tart shell with parchment paper or foil, then fill with pie weights or dried beans. Bake for 15 minutes. Remove the weights and parchment/foil, then continue to bake for another 5-7 minutes, or until the crust is lightly golden. Remove from oven and let cool slightly while you prepare the filling. Reduce oven temperature to 350°F (175°C).

In a medium bowl, combine the chopped rhubarb with 1/2 cup granulated sugar. Let it sit for at least 15-20 minutes, stirring occasionally, to draw out some of the moisture.

While the rhubarb macerates, prepare the custard: In a separate large bowl, whisk together the eggs, egg yolk, 1/2 cup granulated sugar, flour, ground ginger (if using), and salt until smooth.

In a small saucepan, gently heat the heavy cream over medium-low heat until it just begins to simmer around the edges. Do not boil.

Slowly temper the hot cream into the egg mixture: gradually pour about half of the hot cream into the egg mixture while whisking constantly. Then pour the tempered egg mixture back into the saucepan with the remaining hot cream, whisking continuously. Cook over low heat, stirring constantly, until the custard thickens slightly and coats the back of a spoon (do not boil).

Remove from heat and stir in the vanilla extract.

Drain the macerated rhubarb well, discarding any liquid. Pat the rhubarb dry with a paper towel if it seems overly wet.

Spread the drained rhubarb evenly over the bottom of the partially baked tart shell.

Carefully pour the custard mixture over the rhubarb.

Bake in the preheated oven at 350°F (175°C) for 30-35 minutes, or until the custard is set but still slightly wobbly in the center. The crust should be golden brown.

Remove the tart from the oven and let it cool completely on a wire rack before slicing and serving. This will take at least 2-3 hours. The custard will firm up further as it cools.