How to Make It
In a food processor, pulse both flours with the salt to mix. Add the butter and pulse until it is the size of small peas. Sprinkle the water over the flour and pulse just until a dough starts to form. Turn the dough out onto a work surface, gather up any crumbs and knead gently until the dough comes together. Cut the dough in half and pat each piece into a disk. Wrap the disks in plastic and refrigerate until well chilled, about 1 hour.
On a lightly floured work surface, roll out 1 disk of dough to a 12-inch round. Ease the dough into a 9-inch glass pie plate and trim the overhang to 1/2 inch. Freeze for 15 minutes.
In a large bowl, rub the vanilla seeds into the granulated sugar and salt. Add the blueberries, flour, lemon zest and lemon juice and toss well. Scrape the filling into the pie plate.
On a lightly floured work surface, roll out the remaining disk of dough to a 12-inch round. Using three sizes of small round cutters, stamp out decorative holes in the dough, leaving a 2-inch border. Lay the dough over the filling and trim the overhang to 1/2 inch. Press the overhang together to seal, then fold it under itself. Freeze the pie for 1 hour.
Preheat the oven to 375°. Brush the pie with the egg wash and sprinkle with turbinado sugar. Bake for about 1 hour and 15 minutes, until the filling is bubbling and the crust is browned; cover the edge of the pie with foil if it browns too quickly. Let the pie cool completely before serving, at least 5 hours or overnight.