Preheat oven to 450°.
To prepare pastry, lightly spoon flour into dry measuring cups; level with a knife. Combine 1/3 cup flour and ice water, stirring with a whisk until well-blended. Combine 1 2/3 cups flour and salt in a bowl; cut in margarine and shortening with a pastry blender or 2 knives until mixture resembles coarse meal. Add ice water mixture; toss with a fork until moist. Divide dough in half. Gently press each half of dough into a 4-inch circle on heavy-duty plastic wrap; cover with additional plastic wrap. Roll one half of dough, still covered, into an 12-inch circle; freeze 10 minutes. Roll other half of dough, still covered, into an 11-inch circle; freeze 10 minutes.
To prepare filling, combine brown sugar, walnuts, and cornstarch in a large bowl. Combine lemon juice and pears in a medium bowl, and stir in syrup and vanilla. Stir pear mixture into sugar mixture. Remove 1 sheet of plastic wrap from the 12-inch circle, and fit dough into a 9-inch pie plate coated with cooking spray, allowing dough to extend over edge of plate. Remove top sheet of plastic wrap. Combine 2 teaspoons water and egg in a small bowl, and stir well with a whisk. Spoon pear mixture into prepared crust, and brush edges of piecrust lightly with egg mixture. Remove 1 sheet of plastic wrap from the 11-inch circle, and place on top of pear mixture. Remove top sheet of plastic wrap. Press edges of dough together; fold edges under, and flute.
Brush top and edges of pie with egg mixture. Place pie on a baking sheet; cut 5 (1-inch) slits into top of pastry using a sharp knife. Bake at 450° for 15 minutes. Reduce oven temperature to 350° (do not remove pie from oven); bake an additional 45 minutes or until browned. Cool on a wire rack 30 minutes. Serve warm or at room temperature.