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1
Wash plums (no need to peel), cut into 1/2-inch slices, and measure out 9 ounces (1 1/2 cups; 255g) in a large bowl. Add pitted cherries, blueberries, and Cape gooseberries, or whatever mix of fruit you prefer, to bring the total weight to 28 ounces (790g; volume will vary). Toss with sugar, salt, and tapioca starch, folding with a flexible spatula until well combined. Scrape into prepared pie shell and top with remaining dough, as a solid sheet, a
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2
, a
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3
, or
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4
. Trim away excess dough and refrigerate to ensure top crust is completely chilled, about 30 minutes. Meanwhile, adjust oven rack to lower-middle position and preheat to 400u00b0F.
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5
Whisk egg, egg yolk, cream, and salt in a small bowl. Brush over chilled top crust in a thin, even layer. This will give the crust a glossy, golden sheen, but is not necessary in any way.
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6
Place chilled pie on a parchment-lined rimmed baking sheet. Bake until crust is golden, about 1 hour, then loosely cover with tented foil. (Alternatively, an empty baking sheet can be placed on topmost rack of oven to serve as a shield.) Continue baking until filling is bubbling even in the very center of the pie, about 15 minutes more. If crust completely covers filling, bake until pie reaches an internal temperature of 212u00b0F on a digital thermometer.
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7
Cool pie until center of filling is no warmer than 85u00b0F on a digital thermometer, about 3 hours depending on the type of pie plate. (Above that temperature, filling will be runny and thin.) Slice into wedges with a sharp knife, pressing firmly against bottom and sides of pie plate to ensure under-crust is completely cut. Wrapped in foil, leftovers will keep up to 3 days at room temperature; warm 10 minutes in a 350u00b0F oven to revive crust before serving.
