Pre-heat oven to 325 F. In a large bowl combine 1/2 cup powdered sugar, butter and vanilla. Blend well. Stir in flour, nuts and salt until dough holds together. Shape into 1-inch balls. Place an inch apart on ungreased cookie sheets. Bake for 15-20 minutes until set but not brown. Immediately remove from cookie sheets. Cool slightly and roll in powdered sugar. Cool completely and re-roll in powdered sugar.