In a medium skillet, place sugar, water and salt and cook together on a high flame until the sugar begins to change to a golden amber color.

Add milk and butter, and cook for another two to three minutes on a medium flame, until you get a smooth toffee sauce.

Add the dark chocolate and stir until you get a smooth chocolaty mixture. Cool the mixture slightly at room temperature.

Whip the cream into a firm but soft cream and fold gently into the chocolate mixture until a smooth mousse is obtained.

Transfer the mousse to a piping bag with a serrated tip. Cool for 10 minutes in the refrigerator, and then pipe into cups.

Cool the mousse for three to four hours in the refrigerator before serving. Serve sprinkled with chopped nuts and grated chocolate.