Preheat oven to 375°F. Unwrap the larger Slab Pastry Crust disk; roll out on a lightly floured work surface into an 18- x 13-inch rectangle. Wrap dough around rolling pin, and gently fit inside a 15- x 10-inch jelly-roll pan. Turn dough edges under; crimp. Prick bottom and sides of dough with a fork. Line with parchment paper, leaving a 3- to 4-inch overhang around edges of pan. Fill with pie weights or dried beans. Bake 10 minutes. Remove parchment and pie weights. Return crust to oven; bake at 375°F for 5 minutes. Transfer to a wire rack; cool completely, about 30 minutes.

Stir together granulated sugar, honey, ground tapioca, cornstarch, lemon juice, orange zest, orange juice, vanilla, and kosher salt in a large bowl until combined. Gently stir in blueberries until completely coated. Let mixture stand 15 minutes, stirring occasionally.

Meanwhile, unwrap the remaining smaller Slab Pastry Crust disk; roll out on a lightly floured work surface to ¼-inch thickness. Cut out blooms in various shapes and sizes using assorted flower-shaped cookie cutters. Refrigerate until ready to assemble pie.

Spoon blueberry mixture evenly into prepared crust. Arrange assorted flower cutouts over top of pie. Whisk together egg and 1 tablespoon water in a small bowl. Brush mixture over cutouts. If desired, sprinkle flower cutouts with sparkling sugar.

Bake at 375°F until crust and flowers are browned and filling is bubbly, 45 to 50 minutes, covering crust edges with aluminum foil during final 15 minutes of baking to prevent excessive browning, if needed. Transfer to a wire rack; cool completely, about 1 hour.