How to Make It
In a food processor, pulse the flour, cheese and salt. Pulse in the butter until the mixture resembles small peas. Sprinkle with the ice water and pulse until the dough is evenly moistened and just starts to come together. Scrape the dough out onto a work surface and gather it into a ball; divide in half and pat each half into a 6-inch disk. Wrap the disks in plastic and refrigerate until well chilled, about 1 hour.
In a large skillet, heat the olive oil. Add the Swiss chard stems and cook over moderate heat, stirring occasionally, until tender, 8 to 10 minutes. Add the kale and garlic and cook until the kale is wilted, about 3 minutes. Stir in the Swiss chard leaves and season with salt and pepper; cover and cook until wilted, about 3 minutes. Drain the greens in a colander and let cool to lukewarm.
In a bowl, mix the greens, ricotta salata and soppressata. Season the filling with salt and pepper, then stir in the beaten eggs.
Preheat the oven to 400°. On a lightly floured work surface and using a lightly floured rolling pin, roll out 1 piece of the dough to an 11-by-15-inch rectangle, a scant 1/8 inch thick. Ease the dough into a 9-by-13-inch baking pan, pressing the dough into the corners. Refrigerate the bottom crust until chilled, about 15 minutes.
Sprinkle the flour over the chilled crust and scatter the filling evenly over the bottom. Trim any dough that's more than 1/2 inch above the filling. Roll out the remaining dough to an 11-by-15-inch rectangle, a scant 1/8 inch thick. Ease the dough over the filling and trim the overhang to 1/2 inch, then fold the rim over onto itself and pinch to seal. Score the top of the pie in a diamond pattern and brush with the egg wash. Sprinkle with sumac and sesame seeds.
Bake the pie for about 20 minutes, until just starting to brown. Reduce the oven temperature to 375° and bake for 30 to 35 minutes longer, until golden. Let the pie cool for 15 minutes before cutting it into squares; serve warm or at room temperature.