1 1/2 cups sugar
1/4 cup water
2 cups heavy cream
1/4 cup creme fraiche or sour cream
1/2 teaspoon pure vanilla extract
Pinch of coarse salt
Prepare an ice-water bath. Heat sugar and water in a medium saucepan over medium-high heat until mixture boils and sugar dissolves, washing down sides of pan often with a wet pastry brush to prevent crystals from forming. Reduce heat to medium, and cook until sugar turns dark amber, 5 to 7 minutes more. Immediately remove from heat, and carefully whisk in 1 cup cream. Return to medium heat, and cook until sugar melts completely and mixture boils.
Remove from heat, and pour into a bowl set in ice-water bath. Let caramel cool, stirring often, for 10 minutes. Stir in creme fraiche, vanilla, and salt. Cover and refrigerate at least 2 hours or up to 5 days.
Just before using, beat remaining 1 cup cream until stiff peaks form. Gently fold into caramel sauce, using a rubber spatula, until incorporated. Whisk to thicken, about 1 minute.