Line a 9-in. pie plate with bottom pastry; trim even with edge of plate. In a bowl, combine the eggs, sour cream, butter, orange zest and salt. Stir in the rhubarb and apples. Add the sugar and flour; toss to coat. Pour into prepared crust.
Roll out remaining pastry to fit top of pie; place over filling. Trim, seal and flute edges. Cut slits in pastry. Cover edges loosely with foil. Bake at 425° for 15 minutes. Reduce heat to 350°; remove foil. Bake 40-45 minutes longer or until crust is golden brown. Cool on a wire rack.