Melt semisweet chocolate chips and milk chocolate chips in a 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 mixer in a large mixing bowl until thickened. Gradually beat sugar into the cream until the mixture is stiff.

Beat egg whites with 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 the remaining cream-and-egg mixture over the lightened chocolate base and fold together gently; pour into a serving bowl or individual dessert cups.