Make the crust: Blend together flour, butter, and salt in a bowl with your fingertips or a pastry blender or pulse in a food processor until most of the mixture resembles coarse meal with some small, roughly pea-size butter lumps. Drizzle evenly with 4 tablespoons ice water and gently stir with a fork (or pulse in processor) until incorporated. If it doesn't hold together, add more ice water.
Turn mixture out onto a lightly floured surface. Gather all of dough together with scraper and press into a ball, then flatten into a 5-inch disk. Chill dough, wrapped tightly in plastic wrap, until firm, at least 1 hour.
Roll out dough on a lightly floured surface with a lightly floured rolling pin into a 14-inch round, then fit into quiche pan and trim excess dough flush with rim of pan. Chill until firm, about 30 minutes.
Bake pie shell: Lightly prick bottom of shell all over with a fork, then line with foil. Put quiche pan on a baking sheet and bake pie shell at 375 until side is set and edge is pale golden, 18 to 20 minutes. Remove foil and bake shell until bottom is golden, about 10 minutes more. Cool completely in pan on a rack, about 30 minutes.
While shell cooks, make filling: Bring sugar and water to a boil in a 3- to 3 1/2-quart heavy saucepan, stirring until sugar is dissolved. Boil syrup, washing down side of pan occasionally with a pastry brush dipped in cold water and gently swirling pan (do not stir), until mixture is a deep golden caramel, about 10 minutes.
Reduce heat to moderate and carefully add 1 cup cream (mixture will bubble vigorously), stirring until caramel is dissolved. Stir in remaining cup cream and bring just to a simmer.
Whisk together pumpkin purée, spices, and salt in a large bowl. Whisk in hot cream mixture, then add eggs, whisking until combined well.
Pour filling into cooled crust and bake until puffed 1.5 inches from edge and center is just set, about 55 to 60 minutes. Cool in pan on a rack, about 2 hours. Remove side of pan before serving.