To make the crust: Combine flour and salt in a large bowl. Add butter and shortening pieces and mix until the pastry clumps together the size of hazelnuts. Add the water a little at a time until the mixture just holds together. Do not overmix. Remove dough to a floured board. Shape the mass into a disk, wrap with plastic and refrigerate for at least 30 minutes.
Preheat oven to 425 degrees F.
To make the filling: Combine all ingredients except the butter in a large bowl. Transfer mixture to a 9 by 2 inch deep- dish pie pan. Dot with the butter. Roll the dough out to 1-inch larger than the baking dish. Top berries in casserole with the dough. Flute the edges of the dough and cut several slits in the dough to allow steam to escape. Brush with the eggwash.
Bake the pie on a parchment covered sheet pan for 10 minutes, lower the heat to 375 degrees and cook and additional 40 to 50 minutes, or until crust is browned. Let cool slightly, serve warm or room temperature.
Recipe courtesy of David Rosengarten