In a medium bowl, cream butter and sugar until light and fluffy. Stir in the vanilla. Sift together the flour, salt, and cocoa; stir into the creamed mixture. Mix in the pecans until well blended. Cover, and chill for at least 2 hours.
Preheat oven to 350 degrees F (175 degrees C). Roll chilled dough into 1 inch balls. Place on ungreased cookie sheets about 2 inches apart.
Bake for 20 minutes in preheated oven. Roll in confectioners' sugar when cooled.