In electric mixer, cream together the butter and sugar until well mixed.Whisk together the flour and salt. Mix into the butter mixture.Stir in the nuts and vanilla. Roll into small balls. Bake on a parchment paper lined baking sheet in a preheated 350 º F. oven for 15-18 minutes, depending on size, or until lightly browned and baked through. While hot roll in the sifted powdered sugar. Allow to cool and roll once more.Makes about 4 dozen cookies.