Instructions

1. Make the dough: In a food processor, pulse together the flour, sugar, and salt. Scatter over the butter and orange zest and pulse until crumbly with a few almond-size pieces of butter. With the machine running, pour two egg yolks through the feed tube (reserve the whites for another use), then pulse until the dough clears the sides of the bowl. Transfer to a lightly floured work surface and lightly knead until uniform and compact, then divide into two disks of different sizes, about two thirds and one third. Wrap with plastic and refrigerate until firm, at least 1 hour. (The dough will keep, frozen, for 1 month.) 
2. Transfer the disks to a lightly floured work surface and let them soften slightly, about 10 minutes (it should be malleable but cool to the touch). Working quickly, dust the top of the large disk with flour and roll into a 10-inch circle. Drape the dough loosely around the rolling pin and transfer to a 9-inch pastry tin or tart pan with a removable bottom. (If the dough breaks, simply patch up any gaps and tears.) Press the dough firmly into the bottom of the tin, then fold the overhanging dough inward, pressing it into the sides. Flatten the rim so it’s flush with the top of the tin, then use a fork to prick the bottom. Refrigerate or freeze until firm, about 1 hour (or 35–45 minutes if freezing).   
3. Reflour the work surface and roll the smaller disk into an oval measuring 10 inches at the widest point. Using a knife, pizza cutter, or fluted pastry wheel, cut the dough into eight strips of even width (about ½ inch each). Transfer to a baking sheet and refrigerate until firm, about 1 hour.
4. Position a rack in the center of the oven and preheat to 375ºF. In a small bowl, combine the jam and lemon juice (adding more juice to taste if desired), then spread the mixture evenly onto the dough. Using the dough strips, weave a lattice on top of the filling. (The unbaked crostata will keep, wrapped in plastic and refrigerated, for up to 12 hours.)
5. In a small bowl, whisk together the remaining egg and 1 tablespoon of water, then brush the egg wash all over the lattice and perimeter of the dough. Bake, rotating the pan halfway through cooking, until the top is deep golden brown, about 35 minutes. Cool on a wire rack before serving.