Preheat the oven to 400°F (200°C). Scrub the sweet potatoes and poke each several times with a fork. Place on a foil-lined baking sheet and roast for 45–60 minutes, until very soft and a knife slides through easily. Let cool until comfortable to handle.

While the sweet potatoes roast, whisk together the flour, salt, and sugar for the crust in a medium bowl. Add the cold butter cubes and cut them in with a pastry cutter or your fingers until the mixture looks like coarse crumbs with pea-sized bits of butter. Sprinkle in the ice water, 1 tablespoon at a time, tossing gently with a fork, until the dough holds together when pinched but isn’t sticky. Shape into a disc, wrap in plastic wrap, and chill for at least 30 minutes.

Reduce oven temperature to 375°F (190°C). On a lightly floured surface, roll the chilled dough into a 12-inch circle. Gently fit it into a 9-inch pie plate, easing the dough into the corners without stretching. Trim excess and crimp or decorate the edges as desired. Prick the bottom lightly with a fork.

Peel the skins from the roasted sweet potatoes. Measure out 2 packed cups of sweet potato flesh. Mash very well with a potato masher, ricer, or an electric mixer on low speed until smooth and lump-free.

In a large bowl, whisk together the mashed sweet potatoes and melted, slightly cooled butter until smooth. Add the granulated sugar and brown sugar and whisk until fully combined. Whisk in the eggs one at a time, mixing well after each addition. Stir in the evaporated milk, vanilla, cinnamon, nutmeg, ginger (if using), and salt. If the mixture seems very thin, whisk in the optional tablespoon of flour. The filling should be pourable but not runny, similar to a thick custard.

For a flakier bottom crust, line the fitted crust with parchment paper or foil and fill with pie weights or dried beans. Bake at 375°F (190°C) for 10–12 minutes, until the edges are just starting to set. Carefully remove the weights and parchment. If you skip this step, proceed directly to filling the crust.

Pour the sweet potato filling into the prepared crust. Smooth the top with a spatula and tap the pie plate gently on the counter a few times to release any air bubbles.

Bake at 375°F (190°C) for 45–55 minutes. The edges of the filling should be set and slightly puffed, and the center should still have a slight jiggle when the pie plate is gently shaken. If the crust edges brown too quickly, shield them with foil. A knife inserted near the center should come out mostly clean.

Transfer the pie to a wire rack and let it cool completely for at least 2–3 hours. The filling will continue to set as it cools. For the cleanest slices, chill for an additional hour before cutting.

Slice with a sharp knife, wiping the blade between cuts. Serve at room temperature or slightly chilled, plain or with whipped cream or vanilla ice cream.