In a medium saucepan, combine the sugar, cream, corn syrup, and salt. Bring to a boil over medium-high heat, stirring until the sugar dissolved. Cook without stirring until the mixture reaches 245° on a candy thermometer. Immediately pour the mixture over the chocolate and whisk until smooth.
Pour the chocolate mixture into the prepared baking pan. Using a small offset metal spatula, spread the mixture into an even layer. Cool for 20 minutes, or until the caramel is cool enough to handle.
Line 2 baking sheets with parchment paper. Spray a knife with nonstick cooking spray. Cut the caramels into 3/4-inch squares. Transfer them to the baking sheets and allow to set completely—about 6 hours, or overnight. Store the caramels in an airtight container for up to 1 week.