Prepare your baking dish by lining it with parchment paper, allowing some overhang for easier removal later.
In a medium saucepan, combine the granulated sugar, butter, and heavy cream over medium heat. Stir constantly until the mixture melts and begins to boil.
Once boiling, stop stirring and attach the candy thermometer to the side of the pan. Cook the mixture without stirring until it reaches 240°F (soft ball stage).
Remove the saucepan from heat and carefully stir in the Fireball Whiskey, sea salt, and ground cinnamon. Be cautious as it will bubble up.
Pour the mixture into the prepared baking dish and let it sit at room temperature until fully cooled and set, about 3 hours.
Once set, use the overhanging parchment paper to lift the caramel out of the dish. Sprinkle a little additional sea salt on top if desired.
Cut the caramel into small squares or rectangles using a sharp knife.
Wrap each piece in wax paper or cellophane for gift giving or storage, and place in an airtight container.