Instructions

1. Arrange a rack in the middle of the oven and heat the oven to 450°F. Line the bottom and two opposite sides of a 9-inch square baking pan with parchment paper to create a sling. Coat the pan and parchment with cooking spray.
2. Unwrap the 2 pie doughs from 1 box and knead them together on a work surface into one piece of dough. Place the dough in the baking pan and press into an even layer on the bottom.
3. Prick the crust all over with the tines of a fork. Cover with a sheet of parchment paper larger than the pan. Pour pie weights or 2 cups dried beans onto the parchment and spread into an even layer, including the corners.
4. Bake for 15 minutes. Remove the parchment and weights or beans. Return the baking pan to the oven and continue baking until the crust is golden and flaky, 12 to 15 minutes more. Let cool on a wire rack for 10 to 15 minutes while you make the lattice and filling.
5. Reduce the oven temperature to 400°F.
6. Place 5 tablespoons warm water and 3 tablespoons quick-cooking tapioca in a small bowl and stir to combine. Let sit for 15 minutes while you prepare the remaining filling ingredients; you should have a slightly thickened slurry and the granules will be softened but still visible.
7. Meanwhile, use a lightly floured rolling pin to roll out 1 pie dough from the second box (reserve the remaining dough for another use) into a rough 9-inch square about 1/3-inch thick. Cut the square diagonally with a paring knife or pizza cutter into 1/4-inch wide strips. Refrigerate until ready to use.
8. Finely grate the zest of 1 medium lime, then juice the lime until you have 1 tablespoon juice. Place the lime juice, 1 teaspoon of the lime zest (reserve the remaining for garnish), 5 cups frozen or pitted fresh cherries, 1 cup granulated sugar, 1 teaspoon vanilla extract, 1/4 teaspoon ground cinnamon, and 1/4 teaspoon kosher salt in a large bowl and stir until combined.
9. When the tapioca is ready, add to the cherry mixture and stir until evenly incorporated. Use a slotted spoon to transfer onto the crust in an even layer, leaving behind any accumulated juices.
10. Make the lattice top crust: Place 7 or 8 of the cut pastry strips diagonally on top of the filling, spacing them about 1 1/4-inches apart. Repeat laying down pastry strips perpendicular to the first set. Weave the strips together, one at a time, going over and under each other to create the lattice or crisscross pattern. Trim off any excess pastry with a paring knife so the pastry fits just inside the baking dish. (If you have extra strips, you can create a border with them if you’d like.)
11. Whisk 1 large egg and 1 teaspoon water together in a small bowl. Brush it evenly over the pastry lattice. Sprinkle 1 tablespoon demerara or turbinado sugar onto the pastry.
12. Return the baking pan to the oven and bake for 25 minutes. Rotate the baking pan and bake until the lattice is golden brown and the filling is bubbling, 20 to 25 minutes more. Tent the baking pan loosely with aluminum foil if the pastry begins to brown too quickly. Place the pan on a wire rack and let cool completely, about 1 1/2 hours.
13. Place 1/2 cup powdered sugar and 1 teaspoon milk in a small bowl and whisk until smooth and pourable, adding another teaspoon of milk if the mixture is too stiff. Transfer to a sandwich-sized zip-top plastic bag and seal the bag. Snip 1/4-inch off one bottom corner with kitchen shears. Drizzle the icing on top of the bars in a zigzag pattern and sprinkle with reserved lime zest. Let sit until the icing is set, about 10 minutes.
14. Grasping the parchment paper, remove the slab from the baking pan to a cutting board. Cut into 12 to 16 bars.