Preheat oven to 375 degrees. with rack in lower third. Toss peaches, raspberries, granulated sugar, cornstarch, lemon juice, and salt in a large bowl; set aside.
Transfer half the dough to a lightly floured work surface. Roll out dough into a 12-by-16-inch rectangle that is 1/8 inch thick. Coat a 15 1/4-by-10 1/2-inch rimmed baking sheet with cooking spray. Line sheet with parchment paper, leaving a 1-inch overhang on long sides. Transfer dough to prepared baking sheet. Trim edges of dough to hang over sides of baking sheet by 1/2 inch.
Roll out the remaining dough into another 12-by-16-inch rectangle that is 1/8 inch thick. Pour fruit mixture into the dough-lined baking sheet. Cover with remaining layer of dough. Trim edges of dough to hang over sides by 1/2 inch. Fold edges of top layer over edges of bottom layer, and pinch to seal.
Cut about 60 holes out of the top crust using a 1/2-inch round pastry tip (such as Ateco #807), spacing evenly. Whisk together egg yolk and heavy cream in a small bowl. Brush crust with egg wash. Sprinkle with sanding sugar.
Bake until crust turns golden and filling is bubbling, about 1 hour and 10 minutes. (If crust is browning too quickly, tent pie with foil, and continue baking.)
Let cool completely on a wire rack, about 3 hours. Pull up on parchment to remove.