How to Make It
Pulse the flour, butter, and salt in a food processor fitted with a metal blade until the mixture resembles coarse meal, with a few pea-size clumps of butter remaining. Add ⅓ cup ice water. Pulse until the dough is still crumbly but holds together when squeezed.
Press evenly into the bottom and up the sides of a 9-inch pie plate to hang ¼ inch over the rim. Decoratively crimp the edge with a fork or your thumb. Freeze the piecrust until firm, 30 to 40 minutes.
Heat oven to 375° F.
Beat the eggs with the brown sugar, corn syrup, rum, pumpkin pie spice, and vanilla in a large bowl. Stir in the nuts. Scrape the filling into the piecrust and place on a rimmed baking sheet. Bake until the pie is mostly set but still slightly wobbly in the center, 50 to 55 minutes. Let cool completely.
Serve with whipped cream or vanilla ice cream, if desired.
Make-Ahead: Press the dough into the pan, wrap well, and freeze for up to 2 weeks. Or bake the pie and keep, wrapped in plastic, at room temperature for up to 2 days.