In a medium saucepan, bring granulated sugar and ⅓ cup (80 grams) water to a boil over medium-high heat, stirring just until sugar dissolves. Cook, without stirring, until mixture turns light amber in color and a candy thermometer registers 340°F (171°C), 10 to 15 minutes. Remove from heat, and carefully whisk in ⅓ cup (80 grams) cream, butter, and salt. (Mixture will boil vigorously.) Let cool completely.

Add confectioners’ sugar to caramel mixture, whisking until smooth. Whisk in up to remaining 3 tablespoons (45 grams) cream until desired consistency is reached. Use immediately.