On a lightly floured surface, use your hands to slightly flatten Pastry for Single-Crust Pie. Roll dough from center to edge into a circle about 12 inches in diameter. To transfer pastry, wrap it around the rolling pin. Unroll pastry into a 9-inch pie plate. Ease pastry into pie plate, being careful not to stretch pastry. Transfer filling to pastry-lined pie plate. Trim pastry to 1/2 inch beyond edge of pie plate. Fold under extra pastry. Crimp edge as desired, crimping edges high. Do not prick pastry. Set aside.
For filling, in a large bowl, stir together eggs and sour cream. Stir in granulated sugar, the 2 tablespoons flour, the vanilla, and salt. Stir in the rhubarb.
Pour filling into the prepared crust. Cover the edge of pie with foil. Bake in a 450 degree F oven for 15 minutes. Reduce oven temperature to 350 degree F and bake for 20 minutes more.
Meanwhile, in a small bowl, stir together brown sugar and the 1/4 cup flour. Cut in butter until mixture resembles coarse crumbs. Sprinkle mixture over rhubarb filling.
Bake, uncovered, for 20 to 25 minutes more or until filling is set. Cool on a wire rack. Refrigerate within 2 hours; cover for longer storage. Makes 8 servings.