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1
Preheat the oven to 425F.
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2
Prepare the tart dough: Sift the flours, sugar, and salt into the bowl of an electric mixer fitted with the paddle attachment.
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3
On low speed, add the butter, bit by bit, and shortening and mix until the mixture is the consistency of fine cornmeal.
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4
Increase the speed to medium and slowly add the cold water, beating just until the dough forms a ball and pulls away from the sides of the bowl.
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5
Do not overmix.
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6
If the pastry is too dry, beat in a few drops of water on low speed.
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7
Turn the dough out onto a cool lightly floured surface.
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8
Smear the pastry on the surface with the heel of your hand for a final blending and form into a thick flat cake.
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9
Wrap the dough in plastic wrap and refrigerate until just chilled, about 20 minutes.
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10
On a lightly floured surface, rapidly roll out the dough into a rectangle approximately 1/8-inch thick and to fit a large flat baking sheet.
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11
Cover with plastic wrap and refrigerate for 30 minutes.
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12
Cover the pastry with the plum slices in rows, overlapping them slightly and leaving 1-inch border.
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13
Fold the rim of the pastry up to, and slightly overlapping, the plums.
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14
Dust the plums with 1 tablespoon of the sugar.
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15
Bake for 20 to 30 minutes until the crust is browned.
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16
Dust with the remaining 1 tablespoon sugar.
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17
Serve with whipped cream or ice cream.
