Add the chocolate and heavy cream to a heat proof bowland microwave for 30 seconds at a time, mixing each time until smooth. Add to the cooled caramel layer and spread evenly. Sprinkle with sea salt and allow to cool in the fridge for 1 hour. Once cooled, run a large knife under hot water and carefully wipe dry. Cut the slice into 4 large bars long ways, then cut each large bar into 6 smaller bars. Wiping the knife after each cut is a tedious and long way to do this but you get super clean Instagram worthy clean bars.