Add 2 tablespoons of chocolate to each muffin case. Using a pastry brush, brush some of the chocolate up the sides of the case - about halfway. Place the muffin pan in the freezer whilst preparing the filling.
Add the caramels and milk to a microwave-safe bowl, and heat in 30 second intervals, stirring after each one, until melted and smooth. Stir in the salt.
Top the caramel centres with the remaining chocolate (about 1 tablespoon per case), sprinkle with coarse sea salt (optional), and freeze once again until set.