Make the crust: cut butter into flour/sugar/salt, add ice water until dough holds, chill 30 minutes, roll out, and fit into a 9-inch pie plate. Chill 15 minutes.
Preheat oven to 425°F with a rack in the lower third; set the pie plate on a baking sheet.
Whisk pumpkin, condensed milk, eggs, spices, salt, and vanilla until smooth; pour into the crust.
Bake 15 minutes at 425°F, then reduce to 350°F and bake 35-40 minutes more, until edges are set and the center jiggles slightly.
Cool at least 2 hours before slicing. Serve with whipped cream.