Process flour, salt, and sugar together in a food processor until combined, about 3 seconds. Add butter and pulse until butter is the size of large peas, about ten 1-second pulses.

Using a fork, mix sour cream and 1/3 cup ice water in a small bowl until combined. Add half of the sour cream mixture to flour mixture; pulse for three 1-second pulses. Repeat with remaining sour cream mixture. Pinch dough with fingers; if the dough is floury, dry, and does not hold together, add 1 to 2 tablespoons ice water and process until dough forms large clumps and no dry flour remains three to five 1-second pulses.

Turn dough out onto work surface. Divide dough into 2 balls and flatten each into 6-inch disk; wrap each disk in plastic and refrigerate until firm but not hard, 1 to 2 hours, before rolling. (Dough can be refrigerated for up to 24 hours. Let thoroughly chilled dough stand at room temperature for 5-10 minutes before rolling.)

Roll one on a lightly floured surface into an approximately a12-13-inch circle and transfer to a pie plate. Trim the overhang of dough and crimp decoratively around the edges. Roll out the second disc into a 12-inch round or into various sizes (flowers, stripes, etc) as per your design. Wrap all dough in plastic and refrigerate for 20 minutes or until ready to use.

Whisk sugar, eggs, flour, and salt in a large bowl. Stir in rhubarb until evenly coated.

Adjust oven rack to lowest position and heat oven to 375℉. Transfer filling to a chilled dough-lined plate and spread into even layer. Decoratively place prepared pie dough pieces on to of filling. Brush dough pieces thoroughly with extra water (careful not to drag filling onto the dough) and sprinkle with granulated sugar. Refrigerate for 15 minutes.

Place pie on a parchment-lined rimmed baking sheet and bake until crust is set and golden brown, about 50-60 minutes. (If edges of pie begin to get too brown before pie is done, cover loosely with parchment or aluminum foil.) Let cool on a wire rack for 2-1/2 hours before serving.