In a large bowl, whisk together flour and salt. Scatter cubed butter over top, then use a pastry cutter to work it into the flour until the mixture resembles coarse crumbs. Sprinkle 6 tbsp ice water over top, and use a stiff rubber spatula to gently stir and press the dough together. Add more water only if needed to get the dough to stick together. Dump the shaggy mixture onto a lightly floured counter, and divide into two even piles. Gently press each pile into a disk, and wrap with plastic wrap. Refrigerate 1 hour, or up to 48 hours.
Preheat oven to 500ºF and position a baking sheet on the lowest oven rack. Roll out dough between sheets of parchment paper placed on top of a dampened paper towel (this anchors the parchment to the counter). Fit the bottom crust into a 9" pie plate.
In a large bowl, toss the blueberries with the sugar and flour; dump into the bottom crust. Position the top crust over top of the filling, then use kitchen scissors to trim the edges, leaving a 1/2" border. Fold the top border under, and use your fingers to pinch it closed (you can make a pretty pattern if you like). Cut a few steam vents on top of the pie. Brush with egg white, and sprinkle with sugar.
Place pie on top of preheated baking sheet on bottom oven rack. Reduce oven temperature to 425ºF and bake for 25 minutes, then reduce heat to 375º and continue baking until crust is golden and pie filling is bubbling out.