Unlike a traditional apple pie, a slab pie is prepared in a baking sheet and can feed up to 20 people. Its filling is thickened to ensure neat slicing, and it’s topped with a sugary glaze. Rolling out the dough to cover both the bottom and top of this mammoth pie can be problematic, but store-bought crusts proved sturdier than homemade. Gluing two crusts together with water and then rolling the dough into a large rectangle allowed us to get the crust into the large pan without a tear. To improve the bland flavor of the pie crust, we rolled it in crushed animal crackers, which contributed a sweet and buttery flavor to the crust. Flour helped thicken our apple filling, but the result was too pasty. Cornstarch made the filling slimy, but tapioca thickened it well without making it starchy. An 18 by 13-inch nonstick baking sheet is preferred; if using a conventional sheet pan, coat it lightly with cooking spray.