Preheat oven to 350 degrees. Make the crust: Line a 9-inch square baking pan with parchment, leaving an overhang on all sides; butter parchment, excluding overhang. Beat butter and brown sugar on medium speed until pale and fluffy, about 3 minutes. Add flour and table salt, and beat until just combined.
Press dough evenly into pan, and bake until lightly browned, about 30 minutes.
Make the chocolate caramel: Place chocolate in a medium bowl. Heat granulated sugar and water in a small saucepan over medium-high heat, washing sides of pan with a wet pastry brush to prevent sugar crystals from forming, until amber, 10 to 12 minutes. Remove from heat. Add butter, cream, and table salt. Bring to a boil, stirring until smooth. Pour over chocolate. Let stand for 2 minutes. Stir to combine, and let stand until cool, about 10 minutes.
Pour mixture over crust. Refrigerate at least 4 hours, or overnight. Run a knife around edges; lift parchment to remove whole bar from pan. Sprinkle with sea salt. Trim edges, and cut into 16 bars.
Bars can be refrigerated for up to 3 days.