Make the dough: In a small bowl, whisk 1 egg with 6 tablespoons cold water. Set aside.
In a food processor or large bowl, add the flour and butter; using the processor, a pastry cutter, or your hands, work the butter into the flour until only pea-sized crumbs remain. Slowly drizzle in the egg and water mixture, pulsing or stirring it the dough as you pour. Add 1 to 2 more tablespoons water as needed to moisten the dough, stopping when the mixture holds together when pinched (do not overmoisten).
Turn out the dough onto a clean work surface (it will be crumbly) and form it into two neat rectangles: One piece should consist of a little more than 1⁄3 of the total dough, and the other piece should be the remaining scant 2⁄3 of the dough. Wrap the disks tightly in plastic wrap and refrigerate until firmed up slightly and easy to roll out, 20-30 minutes.
Set a rack in the top third of the oven and preheat to 350°. Grease a 9-by-13-inch baking pan with butter and coat it very lightly with flour; set aside.
Remove the larger piece of dough and, working on a lightly floured work surface, roll it out to a thin rectangle about 12 by 16 inches in size. Transfer the dough to the prepared baking pan, tucking the dough neatly into the edges and against the corners (patch any holes with excess dough from the edges). Quickly roll out the remaining (smaller) piece of dough on a lightly floured work surface, and set aside. (If either dough overwarms, place it back in the refrigerator for 5-10 minutes.)
Make the filling: In a large bowl, add 17 of the eggs and whisk until beaten. Stir in the chopped sausage, soppressata, and cheese, then season the mixture generously with black pepper to taste. Pour the egg mixture into the prepared crust, and smooth the filling with a spatula to fill evenly. Carefully top the egg mixture with the smaller piece of dough, then trim the edges with scissors so that neither dough piece has more than 1 inch of overhang. Tuck the edges of the top piece of dough around the edges of the bottom piece, pressing to seal.
In a small bowl beat the remaining 1 egg with 1 teaspoon water. Brush the top dough generously with the egg wash. Cut a small slit in the center of the hole to vent. 8. Bake until a toothpick inserted into the center of the pie comes out clean, about 45 minutes. Remove and let cool slightly. Slice into squares and serve.