For the caramel layer of the filling; combine sugar and water into a saucepan and bring to a boil over high heat. Be sure to brush any sugar crystals that form on the sides of the pan down with a pastry brush dipped in water (otherwise mixture may
seize). Allow to boil for about 11 minutes, or until mixture turns a light amber color. Remove from heat and stir in ½ cup cream and ¾ tsp salt, whisking until smooth. Pour caramel over warm pastry, then chill in fridge until firm, about 15 minutes.