The Expert Hostess 

Melt 1 cup of sugar over medium heat in medium saucepan.  Watch closely. When the sugar turns an amber color, remove from heat and stir in butter (mixture will seize up, and bubble).  Then, mix in cream (mixture will seize again). Return to heat and allow to boil for one minute. Remove from heat and stir in fleur de sel and vanilla.  Pour into glass container and allow to cool. Refrigerate until ready to serve. Sauce can be warmed in microwave to achieve a runny texture when ready to serve.  To serve with crepes, sauce can be poured into a squeeze bottle for easy drizzling. Can be made several days in advance.