Beat butter and ½ cup powdered sugar together in a large bowl. Stir in extract, salt and walnuts, then mix in flour. If dough is not firm, chill until firm enough to hold its shape. Shape into 1-inch balls and place on ungreased cookie sheet. Bake in an oven preheated to 350°F for about 15 minutes or until bottom edges begin to brown. Remove from oven, let cool 5 minutes and then roll cookies in a bowl of powdered sugar to coat. Set aside to fully cool.
