Put water into bottom part of a double boiler. Bring to a simmer and be sure the water does not touch the bottom of the top part. Let the top part heat.
Put cream, sugar, and salt into a saucepan. Stir-cook until sugar dissolves and cream is hot. Turn off heat.
Put chocolate (both) and Cognac into a small enameled pan. Bring to a boil, remove, cover