In a heavy saucepan, combine sugar and water over medium-low heat until the sugar dissolves. Increase the heat and bring to a boil, swirling the sauce pan gently, but not stirring. Simmer until the mixture is syrupy and a deep caramel color, about 5-10 minutes.
Remove mixture from heat and whisk in butter and cream, being mindful that the mixture will spit and sizzle, so be careful. Whisky vigorously until it reaches a smooth, sticky consistency. Finally, whisk in vanilla and fleur de sel. Set aside to cool.
If you've tried this recipe, come back and let us know how it was!
Notes
Use more or less depending on your tastes. Go slow- you can always add more.