Combine flour and 1/2 teaspoon salt; cut in shortening with a pastry blender until mixture is crumbly. Sprinkle cold water (1 tablespoon at a time) evenly over surface; stir with a fork until dry ingredients are moistened. Shape into a ball; cover and chill.
Roll dough into a 12-inch circle on a lightly floured surface. Place in a 10-inch pieplate; trim off excess pastry along edges. Fold edges under, and flute.
Combine butter and 1/3 cup brown sugar; stir in pecans. Press mixture over pastry shell. Bake at 425° for 5 minutes. Let cool on a wire rack. Reduce oven temperature to 350°.
Combine eggs and next 8 ingredients in a large mixing bowl; beat at medium speed of an electric mixer until blended. Pour mixture over praline layer in pastry shell. Bake at 350° for 50 minutes or until pie is set. Let cool on wire rack. Top with whipped cream, if desired.