Best-Ever Rhubarb Pie

In a large bowl, combine rhubarb, sugar, cornstarch, lemon juice, and salt. On a lightly floured surface, roll each piece of dough out into two 12" rounds.  Fit one round into a 9" glass pie plate and fill with rhubarb mixture. Dot evenly with butter, then cover pie with remaining round and trim overhang to 1”. Fold edges of top dough under and crimp together.  Using a sharp knife, make five 1" slits in a circle in the center of the top crust. Freeze pie for 30 minutes. Preheat oven to 375° with a rack in the middle and the bottom third. Brush top crust all over with egg wash and sprinkle generously with sanding sugar.  Bake pie on middle rack, with a foil-lined baking sheet on bottom rack to catch juices, about 1 hour. Check to see if top crust is browning too quickly and tent with foil if necessary. Continue to cook, checking every 10 minutes to see if top crust needs to be tented, for about 30 minutes more, until bubbling in center and bottom crust is golden. Transfer pie to a rack to cool completely.