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Preheat the oven to 350°F.
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For the crust, cream the butter and sugar until light in the bowl of an electric mixer fitted with the paddle attachment.
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Combine the flour and salt and, with the mixer on low, add to the butter until just mixed.
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Dump the dough onto a well-floured surface and gather into a ball.
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Flatten the dough with floured hands and press it into a 9 x 13 x 2" baking sheet, building up a 1/2" edge on all sides.
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Chill.
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Bake the crust for 15 to 20 minutes, until very lightly browned.
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Let cool on a wire rack, leaving the oven on.
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For the filling, whisk together the eggs, sugar, lemon juice, and flour, and pour into the crust.
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Bake for 30 to 35 minutes more, until the filling is set.
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Let cool to room temperature.
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Cut into triangles and dust with confectioners' sugar.