Melt chocolate in top of a double boiler over boiling water. Add sugar, hot water, and milk, stirring well.
Beat egg yolks until thick and lemon colored. Gradually stir one-fourth of chocolate mixture into yolks; add to remaining chocolate mixture, stirring constantly. Cook over boiling water 15 minutes or until thickened and bubbly. Stir in salt. Remove from heat. Cool completely. Stir in vanilla.
Beat egg whites (at room temperature) until stiff, but not dry. Gently fold beaten whites into chocolate mixture.
Beat whipping cream until soft peaks form. Fold whipped cream into chocolate mixture. Chill.