Step 4
Prepare caramel filling: In a large saucepan, bring sugar, water and corn syrup to a boil. Stir or swirl the pan occasionally, until mixture is a medium amber color, about 12 minutes. Remove from the heat. Caramel will continue to cook and darken off of the heat. Carefully but quickly whisk in the butter, cream, creme fraiche and salt until smooth (mixture will bubble up). Pour hot caramel into tart, and allow to cool and set, at least 1 hour.