In a large bowl mix sugar, mayonaise and vanilla until well blended. Stir in flour mixture and add 1/2 cup pecans. (dough will be thick and sticky.) Press into well greased 8 inch square baking pan.
Sprinkle with remaining nuts and press into dough. Bake in 350 degree F oven 15 minutes or until pick inserted in center comes out clean. Cool in pan on rack. Cookies are soft while hot but firm when cool.
