Whisk together cream cheese and whipping cream in a small bowl until smooth. Set aside.
Cook sugar and 2/3 cup water in a heavy 3 1/2-quart saucepan over medium-low heat, stirring constantly, 5 minutes or until sugar dissolves. Increase heat to high, and bring mixture to a boil without stirring. Using a pastry brush dipped in hot water, brush down any sugar crystals on sides of pan. Cook, without stirring, 10 minutes or just until syrup turns a deep amber color.
Whisk in butter gradually; gradually whisk in cream cheese mixture until smooth. Remove from heat; cool 10 minutes, whisking occasionally.