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1
Preheat oven to 375F, with rack in lower third.
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2
Gently toss peaches, raspberries, granulated sugar, cornstarch, lemon juice, and salt in a large bowl.
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3
On a lightly floured surface, roll out each disk of dough to a 16-by-12-inch rectangle, 1/8 inch thick.
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4
Transfer one rectangle to a 15-by-10-inch rimmed baking sheet.
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5
Trim excess dough to a 1/2-inch overhang.
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6
Transfer remaining rectangle to a parchment-lined baking sheet.
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7
Refrigerate or freeze both until firm, about 30 minutes.
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8
Pour fruit mixture into dough-lined baking sheet, and spread into an even layer.
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9
Cover with remaining rectangle of dough.
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10
Trim edges of top piece of dough to 1/2-inch overhang.
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11
Fold edges of top layer over edges of bottom layer, and pinch to seal.
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12
Working in rows, cut about 60 holes from top crust using a 9/16-inch plain tip (such as Ateco #807), spacing evenly.
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13
Whisk together yolk and cream in a small bowl.
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14
Brush crust with egg wash. Sprinkle with sanding sugar.
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15
Bake until crust turns golden and filling is bubbling, about 90 minutes.
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16
(Tent with foil if crust is browning too quickly.)
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17
Let cool completely on a wire rack, about 3 hours, before cutting and serving.
