2 cups granulated sugar
12 tablespoons unsalted butter, at room temperature and cut into pieces
1 cup heavy cream, at room temperature
1 tablespoon fleur de sel (or another sea salt)
Melt the sugar over medium-high heat. Stir until all the sugar is melted. As soon as the sugar turns amber in color add your butter and whisk vigorously. It will bubble up aggressively but keep whisking until all the butter has melted. Remove pan from the heat and slowly pour in the cream while whisking vigorously. The caramel is going to bubble aggressively again, so be careful! Whisk until all the cream is incorporated and then whisk in the fleur de sel. Set the sauce aside to cool for 15 minutes prior to pouring it into a glass jar to cool completely. You can refrigerate the sauce for up to 2 weeks, but you will need to warm it before using.