Grease a 13-in. x 9-in. pan with butter; set aside. In a large heavy saucepan, combine the sugar, corn syrup and vinegar. Cook and stir over medium heat until sugar is dissolved. Cook, without stirring, until a candy thermometer reads 290° (soft-crack stage).
Remove from the heat; stir in baking soda. Pour into prepared pan but do not spread; cool. Break into pieces.
Dip each candy halfway into white candy coating; allow excess to drip off. Place on waxed paper-lined baking sheets until set. Dip plain half of candies into dark chocolate coating; allow excess to drip off. Return to waxed paper until set. Store in an airtight container.
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