For the crust, mix the flour and 1/4 teaspoon salt. Cut in the cold butter with a pastry cutter or your fingertips until the largest pieces are the size of peas. Sprinkle in ice water a tablespoon at a time, stirring with a fork, until the dough holds together when squeezed. Shape into a disk, wrap and chill for at least 1 hour.
Roll the dough into a 12-inch circle on a floured surface and fit it into a 9-inch pie dish. Trim and crimp the edges. Chill for 15 minutes while you heat the oven to 400°F (200°C).
Line the crust with parchment and fill with pie weights or dried beans. Bake for 15 minutes, remove the weights and parchment and bake 5 minutes more. Lower the oven to 350°F (175°C).
Whisk the pumpkin, brown sugar, eggs, yolk, evaporated milk, spices, vanilla and remaining salt until smooth.
Pour the filling into the warm crust and bake for 40–50 minutes, until the edges are set and the center still jiggles slightly. Cover the crust edges with foil if they brown too quickly.
Cool the pie on a rack for at least 2 hours, then refrigerate until fully set, preferably overnight.