Make crust in medium mixing bowl, by combining flour, salt, and oil until "crumby." Drizzle in just enough cold water, 2-3 tablespoons, to make a smooth, slightly sticky mixture. Flour surface you will use to roll out dough. This amount makes enough for an 8-inch pie, if larger, make more dough. Roll out [larger] bottom crust and nestle it into the pie pan. Dump remaining dough on floured surface, and use the mixing bowl to prepare the filling: Combine blueberries, flour water and sugar in the same bowl you used to make the crust, tossing very lightly to coat each berry.
Pour coated berries into bottom crust. Roll out top crust, making it just a half-inch larger than top edge of pan. Place on top of filling.
Shape edge by bringing bottom crust up over top crust, and pinching between your thumbs and pointer fingers. Cut a vent hole in top crust, being careful not to pierce bottom crust. Apply crisping, spreading butter over top crust, then sprinkle evenly with sugar.
Bake in preheated 400 degree oven for 30 minutes, until top is golden, and filling is bubbly. Allow to cool at least 15 minutes, so filling sets. To speed the process, place baked pie in front of a fan on low setting. Serves 6.