Preheat oven to 325 degrees.
Beat butter, shortening and one cup powdered sugar until fluffy.
Add salt and vanilla, and beat well. Stir in flour, 1/3 at a time. Mix in nuts.
Shape dough into 1" balls. Bake for 20 - 30 minutes, until lightly colored.
While warm, roll in remaining one-half cup powdered sugar, and cool on a wire rack. When cool, roll in remaining sugar.
To freeze, layer Mexican Wedding Cakes in freezer food storage containers in rows separated by sheets of waxed paper. Cookies will stay fresh from 4 to 6 weeks. After thawing, roll cookies in powdered sugar before serving.