1 cup white sugar
1 cup dark corn syrup
1 tablespoon vinegar
1 tablespoon baking soda
1 pound chocolate confectioners' coating

Butter a 9x13 inch baking dish.
In a medium saucepan over medium heat, combine sugar, corn syrup and vinegar. Cook, stirring, until sugar dissolves. Heat, without stirring, to 300 to 310 degrees F (149 to 154 degrees C), or until a small amount of syrup dropped into cold water forms hard, brittle threads. Remove from heat and stir in baking soda. Pour into prepared pan; do not spread. Mixture will not fill pan. Allow to cool completely.
In the microwave or over a double boiler, melt coating chocolate, stirring frequently until smooth. Break cooled candy into bite sized pieces and dip into melted candy coating. Let set on waxed paper. Store tightly covered.

Source: allrecipes.com