Line a 9 x 13-inch baking pan with parchment paper, making sure it goes up the sides slightly for easy removal.
In a large, heavy-bottomed saucepan over medium heat, combine granulated sugar, unsalted butter, and evaporated milk. Stir constantly until the mixture comes to a boil.
Once boiling, continue cooking, stirring frequently, until the mixture reaches 234°F on a candy thermometer. This should take about 5 minutes.
Remove the saucepan from the heat. Stir in caramel bits until they are completely melted and fully combined.
Add marshmallow fluff, vanilla extract, and flaky salt. Stir until the mixture is smooth and everything is well incorporated.
Pour the mixture into the prepared pan, spreading it out evenly. If desired, sprinkle a little extra flakey salt over the top.
Let the fudge cool at room temperature for about 2 hours, or until fully set. Cut into squares and enjoy!