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.