Line bottom and sides of an 8-inch square baking pan with parchment paper. Lightly spray the parchment with cooking oil. NOTE: You must use parchment paper because it prevents the caramel from sticking to it. Wax paper and plastic wrap won't work.
Bring cream, butter, and fleur de sel to a boil in a small saucepan, then remove from heat and set aside.
Boil sugar, corn syrup, and water in a separate medium saucepan, stirring until sugar is dissolved. The caramel needs your constant attention so don't try to multitask (something I tend to do while cooking which results in burnt food). Next, boil the liquid without stirring and instead gently swirl the pan until the mixture is a light golden caramel.
Carefully stir in cream mixture (mixture will bubble up) and simmer, stirring frequently, until caramel registers 248°F on thermometer, 10 to 15 minutes. NOTE: The longer you cook the caramel and the hotter the caramel becomes, the harder your candy will be when it cools. Big Onechan tested this theory when she ended-up with very hard caramel-like-toffee.
Pour into baking pan and cool 2 hours. Cut into 1-inch pieces, then wrap each piece in a 4-inch square of wax paper, twisting 2 ends to close.
Notes
Recipe compliments of Gourmet Magazine.
Recipe by Bebe Love Okazu at https://bebeloveokazu.com/2011/01/21/caramel/