Grease a 9 x 7 or similar size pan. Line with parchment, then grease again, to easily remove the cooled caramel. Leave an overhang of paper on the side to act as handles.
Add all of the ingredients except the vanilla and sea salt to a medium heavy saucepan.
Slowly bring to a boil over medium heat, stirring constantly until a candy thermometer reaches 234 -240°F. This will take about 10 - 15 minutes. Large bubbles will form at the edges of the pot. Cook, still stirring constantly for 2 minutes at 234 -240°F.
Remove from the heat and immediately stir in the vanilla.
Pour into the prepared pan and allow to cool and firm up. Sprinkle with sea salt. Cut into bite size pieces and wrap in wax paper.
Chilling the caramel will make it easier to cut. Place the pan in the refrigerator for 20 minutes, remove the caramel using parchment handles. Use a sharp knife to cut into pieces.If using this caramel for another recipe, omit the final sea salt step.