Grease 9x9-inch pan and line with foil. Also grease foil. Combine flour, sugar and salt. Cut in butter until crumbly. Sprinkle in cold water, 1 tablespoon at a time, mixing with fork until dough holds together.
Press evenly into pan. Prick with fork and bake at 375 degrees for 15 to 20 minutes until golden. Cool crust completely.
When crust is cool, preheat oven to 375 degrees again and prepare filling. Coarsely chop 1/2 cup nuts. Set aside. In food processor, blend redessertsing nuts and brown sugar until finely ground.
Combine nut mixture with egg and vanilla. Spread evenly over cooled crust. Sprinkle with reserved nuts. Bake at 375 degrees for 20 minutes or until filling is set. Cool completely. Remove from pan and cut into 32 wedges.