Mix shortening, sugar, and egg. Stir in buttermilk and vanilla. Sift together the flour, cocoa, salt & soda. Stir into mixture and blend well. Mix in nuts and chill at least 1 hour. Heat oven to 400° and drop rounded teaspoonfuls of dough 2 in. apart onto lightly greased baking sheet. Bake 8-10 minutes or until done.