Mix the 1 cup sugar, salt and half-and-half in a heavy-bottom saucepan. Heat
to scalding, stirring occasionally and being careful not to boil.
Slowly whisk about
a cup of the hot half-and-half mixture into the eggs, then slowly whisk the egg
mixture back into the saucepan. Cook over medium-low heat, stirring constantly,
until the mixture thickens slightly.
Remove from heat and stir in vanilla extract.
Melt the chocolate and 1/2 cup sugar in the top of a double boiler over barely
simmering water; stir until smooth.
Pour the chocolate mixture into the custard;
stir until thoroughly blended.