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1
Blend together flour, butter, shortening, and salt in a bowl with your fingertips or a pastry blender (or pulse in a food processor) just until mixture resembles coarse meal with some small (roughly pea-size) butter lumps. Drizzle 3 tablespoons ice water evenly over mixture and gently stir with a fork (or pulse) until incorporated.
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2
Squeeze a small handful of dough: If it doesn't hold together, add more ice water, 1/2 tablespoon at a time, stirring (or pulsing) until incorporated, then test again. Do not overwork dough, or pastry will be tough.
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3
Turn out mixture onto a work surface and divide into 4 portions. With heel of your hand, smear each portion once or twice in a forward motion to help distribute fat. Gather dough together (with pastry scraper, if using) and press into a ball, then flatten into a 5-inch disk. If dough is sticky, dust lightly with additional flour. Chill dough, wrapped tightly in plastic wrap, until firm, at least 1 hour.
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4
Roll out dough into a 13-inch round on a lightly floured surface with a lightly floured rolling pin. Fit dough into a 9-inch pie plate and trim, leaving a 1/2-inch overhang, then fold overhang under slightly. Crimp edge decoratively. Chill shell until firm, about 30 minutes.
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5
Put oven rack in middle position and preheat oven to 375u00b0F.
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6
Lightly prick shell all over with a fork. Line shell with foil and fill with pie weights. Bake until pastry is pale golden along rim and set underneath weights, 15 to 20 minutes. Carefully remove foil and weights and bake shell until bottom and side are golden, about 15 minutes more. Cool completely in pie plate on a rack, about 20 minutes.
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7
Bring corn syrup, 3/4 cup sugar, and 2 tablespoons water to a boil in a 11/2- to 2-quart heavy saucepan over moderate heat, stirring until sugar is dissolved. Boil mixture, without stirring, swirling pan occasionally, until it melts into a deep golden caramel, 7 to 9 minutes.
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8
Remove saucepan from heat and add butter, vinegar, and a pinch of salt, swirling pan until butter is melted. Add 1/3 cup cream and vanilla and simmer, stirring, 1 minute (sauce will be golden brown). Cool sauce to warm.
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9
While sauce is cooling, sprinkle gelatin over remaining 2 tablespoons water in a small saucepan and let stand 1 minute to soften, then heat over low heat until dissolved. Stir into butterscotch sauce and cool to room temperature.
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10
Beat egg whites with a pinch of salt in a large bowl with an electric mixer until they hold soft peaks, then add remaining tablespoon sugar and continue to beat until whites just hold stiff glossy peaks. Fold in butterscotch sauce gently but thoroughly.
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11
Beat remaining cream with cleaned beaters until it just holds stiff peaks, then fold into butterscotch mixture gently but thoroughly. Gently pour chiffon into cooled pastry shell, letting it mound, and chill, uncovered, until set, at least 2 hours.
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12
Cook pecans in butter with salt in a small heavy skillet over moderate heat, stirring frequently, until golden, about 5 minutes. Remove from heat and cool nuts completely.
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13
Let pie stand at room temperature, about 30 minutes. Just before serving, sprinkle cooled nuts over top of pie.
