Line an 8x8-inch pan with aluminum foil and set aside.
In a medium saucepan, combine the sugar, heavy cream, and corn syrup and bring to a boil. Boil, without stirring, until the mixture reaches 238°F using a candy thermometer.
Quickly transfer to the bowl of a stand mixer and beat on low for 1 minute, then increase the speed to medium-high and beat for 6 more minutes or until mixture loses its sheen. Then mix in the vanilla and salt.
Transfer the mixture to the prepared pan, spreading evenly, and refrigerate for 30 minutes until set.
Chop up the chocolate and add to a small microwave-safe bowl and microwave on 30-second intervals, stirring between each one until chocolate is smooth.
Spread the melted chocolate over the top of the set candy, place back in the fridge until chocolate hardens.