Preheat oven to 425 degrees F.
Roll out the dough 1/8-inch thick on a lightly floured surface, fit it into a 9-inch pie plate, and crimp the edge decoratively. Line the shell with foil, fill the foil with rice, and bake the shell in the middle of the oven for 10 minutes. Remove foil carefully and bake for 3 to 5 minutes more, or until it is completely pale golden.
Raise oven temperature to 450 degrees F.
Make the filling: In a large bowl stir together the sugar, tapioca, pinch of salt, vanilla, rhubarb, strawberries, and the butter until the mixture is combined well and let filling stand, stirring occasionally, for 15 minutes.
Make the streusel topping: In a large bowl stir together the brown sugar, flour, butter, cinnamon, walnuts, and a pinch of salt and blend the mixture until it resembles coarse meal. Spoon the filling into the shell, sprinkle with the streusel topping around the outer 2-inches of the filling, leaving the center exposed, and brush the edge of the shell with some of the egg wash. Bake the pie on a baking sheet in the lower third of the oven for 15 minutes, reduce the heat to 350 degrees F., and bake the pie for 50 minutes to 1 hour, or until the filling is bubbling and the rhubarb is tender. Brush the exposed (center) portion of the filling with the jelly and let the pie cool on a rack for 2 hours.
Recipe courtesy of Gourmet Magazine