1. To make crust*, sift together the sifted flour and salt into a mixing bowl.. Cut in the shortening until particles are the size of small peas. Sprinkle 3 to 4 tablespoons cold water over mixture, while tossing and stirring with a fork. Add water to driest particles, pushing lumps to side, until dough is moist enough to hold together. Form into a ball. Flatten to 1/2-inch thickness; smooth edges. Roll out on floured surface to a circle 1-1/2 inches larger than inverted 9-inch pie pan. Fit into pan. Fold edge to form rim; flute. Prick. Bake at 450 degrees F. for 10 to 12 minutes until golden brown. Cool.
2. To make filling, combine sugar and cornstarch in a saucepan. Add butter, lemon rind, lemon juice and egg yolks. Stir in milk; cook over medium heat, stirring constantly, until thick. Cool. Fold in sour cream. Spoon into baked shell. Chill at least 2 hours. Serve with whipped cream and chopped walnuts.
*or use a 9-inch pie shell baked according to package directions.