To make the crust, combine the flour, salt, and sugar in a mixing bowl. Cut the butter into ½-inch (1.25 cm) pieces, then add to the flour and mix to a coarse meal. Add the sour cream and the extract (if you’re using it), and combine just until the ingredients come together into a dough.

Divide the dough to create two flat disks; wrap these in cling film or fit in a tightly sealed container and let them rest for at least 15 minutes in the fridge, or until needed.

To make the filling, cut the pumpkin into quarters, then peel. It will take about four to five strokes with a vegetable peeler to get past the multiple skins and sinew of the pumpkin.

Completely remove any foamy portions attached to the unripe seeds. Cut the quarters in half, then cut into ¼-inch-thick (6 mm) slices to resemble apple slices, and reserve 2½ pounds (1.1 kg) (a scant half) of them for the pie. Save the remaining pumpkin for another purpose.

Toss the pumpkin with the sugar, vinegar, cornstarch, spices, and salt, and allow to macerate for 20 minutes, tossing occasionally.

Transfer the macerated pumpkin and the liquid, scraping out the bowl, to a 12-inch (30 cm) cast-iron skillet (or similar). Heat to a brisk simmer, stirring occasionally, then turn off the heat and cool for 15 minutes to evaporate some water. It should look like prepared pie filling.

Preheat the oven to 350°F (180°C). Roll out the bottom piecrust and set in an ungreased pie pan. Transfer the filling to the lined pan. Roll out the top crust and gently place it on top of the filling, folding the top crust under the bottom crust’s edges.

Crimp the edges, brush liberally with the egg white, sprinkle with the sugar (if you’re using it), cut a few slits in the top to allow air to escape, then bake 45 to 55 minutes. Allow the pie to cool to room temperature, then serve.