Preheat oven to 375 degrees. Line a rimmed baking sheet with foil, then parchment. Stir together fruit, granulated sugar, lemon juice, salt, and cornstarch.
Roll out pate brisee into a 13-inch round, about 1/8 inch thick, on a lightly floured surface. Transfer to baking sheet. Arrange fruit in center, leaving a 2-inch border. Fold over border to enclose fruit, leaving center open. Brush crust with egg, and sprinkle with sanding sugar.
Bake until golden brown and bubbling in center, about 1 hour 10 minutes. Let cool on baking sheet 10 minutes, then slide galette on parchment onto a wire rack. Let cool completely. Serve with whipped cream.