01 - Preheat oven to 350°F. Line a 9x9 inch baking pan with parchment paper, allowing overhang on opposite sides for easy removal.
02 - Combine graham cracker crumbs, melted butter, sugar, and salt in a medium bowl. Press mixture firmly and evenly into the bottom of the prepared pan. Bake for 10 minutes until lightly golden. Set aside to cool slightly.
03 - Beat cream cheese in a large bowl until completely smooth. Add sour cream and sugar, mixing until creamy and well combined. Add eggs one at a time, beating well after each addition. Blend in vanilla extract and flour, mixing until just incorporated.
04 - Pour filling over the cooled crust and smooth the top. Bake for 35 to 40 minutes until edges are set and the center appears slightly jiggly. Cool completely on a wire rack, then refrigerate for at least 2 hours until firm.
05 - Combine sugar and water in a medium saucepan over medium heat. Swirl the pan gently (do not stir) until sugar dissolves and mixture turns deep amber in color. Remove from heat immediately. Carefully whisk in butter until melted, then slowly whisk in heavy cream until smooth. Stir in sea salt if using.
06 - Let caramel cool slightly until thickened but still pourable. Pour evenly over the chilled cheesecake layer. Refrigerate for 1 additional hour until caramel is set.
07 - Using the parchment overhang, lift the bars from the pan. Cut into 16 equal squares with a sharp knife, wiping the blade clean between cuts for neat edges. Serve chilled or at room temperature.