Line an 8x8x2-inch baking pan with parchment paper. Cut 2 pieces of parchment paper to fit the pan, leaving an overhang on all sides; set aside.

In a Dutch oven over medium heat, combine sugar, heavy cream, corn syrup, butter, and kosher salt stirring frequently until the butter melts and the mixture begins to boil.

Attach a candy thermometer to the pot. Continue cooking and stirring until the temperature reaches 245 degrees. Remove from heat and stir in vanilla extract.

Immediately pour into the prepared pan. Sprinkle fleur de sel over the top.

Let the caramel harden for 4-6 hours or overnight. Lift the caramel out of the pan using the parchment paper handles. Cut into pieces using kitchen shears or a warm knife. Wrap individual pieces in parchment or wax paper. Store at room temperature.