Fleur De SelUse softened unsalted butter to grease an 8x8 pan. Cut two strips of parchment paper to fit the pan, leaving an overhang on each side and buttering each piece. Set aside. Combine sugar, heavy cream, corn syrup, salted butter, and fine sea salt in a 3-quart saucepan. Stirring frequently, cook on medium heat until the butter melts and the mixture starts to boil. Clip on a candy thermometer. Continue cooking and stirring until the temperature reaches 245ºF. (This will take about 30 minutes.) Lower the heat as needed to prevent bubbling over. As soon as the mixture reaches 245ºF, remove from heat and stir in the vanilla bean paste (see note). Immediately pour into the prepared pan. Sprinkle the fleur de sel over the top. Let the caramels set for at least two hours and up to overnight. Lift the caramel out of the pan using the parchment paper. Cut into pieces using kitchen shears. Wrap individual caramels in pieces of waxed paper. Store at room temperature. Note: To make chocolate caramels, omit the vanilla bean paste. Stir together 1/2 teaspoon vanilla extract with 1/4 teaspoon espresso powder. Add this mixture plus 3 ounces melted unsweetened chocolate in place of the vanilla bean paste.