Pour about 3 tablespoons of the caramel into the middle of each tart pan or pour all the caramel into one large pan, leaving a little bit of crust around the outsides (this will help the chocolate seal the tart later). Place in the freezer for about 5 minutes, until caramel is hard.
While caramel hardens, melt chocolate in a double boiler. When caramel is hard, pour chocolate over the top of each caramel tart, covering all the caramel and smoothing the chocolate out to the sides of the tart. Sprinkle a pinch of coarse sea salt in the middle then place in the fridge for about 10 minutes, until chocolate is set and has hardened.
Before serving, remove from refrigerator for 10-15 minutes then run a knife under hot water for a bit, wipe dry then slice.