Butter the sides of a heavy saucepan; add the first five ingredients. Cook and stir over medium-high heat until sugar is dissolved. Cook, without stirring, until a candy thermometer reads 238° (soft-ball stage). Remove from the heat. Cool, without stirring, until mixture reaches 110°.
Transfer to a large bowl; add the cinnamon, vanilla and salt. Beat until light-colored and stiff enough to knead, about 2 minutes. Knead mixture in bowl for 2 minutes or until smooth. Roll into 1-in. balls; cover and freeze for 20 minutes.
In a microwave, melt chips and shortening; stir until smooth. Dip balls in chocolate; allow excess to drip off. Roll in nuts if desired. Place on waxed paper; let stand until set.