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1
Puree 1 1/2 cups grapes in processor.
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2
Strain grape puree, pressing on solids to extract as much juice as possible.
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3
Pour 1/2 cup grape juice into large bowl; discard any remaining juice.
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4
Cut 4 3/4 cups grapes lengthwise in half; add all grapes to juice in bowl.
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5
Add sugar, 6 tablespoons flour, and lemon juice; toss to blend well.
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6
Let stand 30 minutes, stirring occasionally.
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7
Preheat oven to 375F.
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8
Line 2 rimmed baking sheets with parchment paper.
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9
Roll out 1 pastry sheet on lightly floured surface to 11-inch square.
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10
Cut off just enough pastry from corners to form rough circle.
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11
Transfer pastry to 1 prepared baking sheet.
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12
Sprinkle 1 tablespoon flour over center of pastry, leaving 2 1/2-inch plain border.
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13
Spoon half of grape mixture, including juices, into center of pastry.
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14
Fold pastry edges up over grapes, forming 2- to 2 1/2-inch border.
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15
Dot grapes with 1 tablespoon butter.
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16
Repeat with remaining ingredients for second tart.
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17
Bake tarts until crusts are golden brown and grape juices are bubbling, about 45 minutes (crust border will unfold slightly).
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18
Cool tarts to room temperature.
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19
(Can be prepared 6 hours ahead.
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20
Let stand at room temperature.)
