Cream butter; gradually add sugar, beating well. Stir in milk, vanilla, peppermint oil, and salt. Chill mixture overnight or until firm. Shape into 3/4-inch balls.
Place paraffin, if desired, in top of double boiler over boiling water. Add chocolate, stirring until melted. Using 2 forks, quickly dip balls one at a time into melted chocolate mixture. Place dipped candies on waxed paper, and refrigerate until chocolate is firm.