To make pastry, in a large bowl sift together flour and Granulated sugar|Sugar. Cut in butter until mixture resembles coarse meal. Stir in egg. Knead lightly to evenly distribute butter. Shape into ball, dust with flour, wrap in wax paper and refrigerate 1 hour. Roll out dough and fit in 10" tart pan with removable bottom. Prick pastry with fork, line with foil and fill with weights or beans. Bake at 400' for 10-15 minutes. Let cool. To make filling, combine all ingredients in food processor and puree. Pour into baked pie shell and bake at 375' for about 20 minutes. Let cool. Remove from pan. Sprinkle with walnuts and serve with whipped cream.