Melt semisweet chocolate chips and milk chocolate chips in heavy saucepan over very low heat while stirring. Stir coffee into the melted chocolate, remove from heat, and cool to room temperature.
Beat egg yolks, one at a time, into the chocolate mixture.
Beat heavy cream with an electric hand mixer in a large mixing bowl until thickened. Gradually beat sugar into the cream until the mixture is stiff.
Beat egg whites with the salt in a separate glass or metal bowl until stiff peaks form; fold into the cream mixture. Take about 1/3 of the resulting mixture and stir into the chocolate mixture. Scrape remaining cream-and-egg mixture over lightened chocolate base and fold together gently; pour into a serving bowl or individual dessert cups.
