Preheat oven to 300 degrees F. Thoroughly grease a 10-inch springform pan.
Combine coffee, salt, and sugar in a saucepan over medium heat; stir until the sugar has dissolved completely, and set aside.
Break each chocolate bar into six pieces. (Feel free to chop these pieces smaller; the smaller the pieces, the faster your chocolate will melt.) Place the pieces in a large, microwave-safe bowl.
Using 30-second increments, melt chocolate in the microwave. Remove from the microwave and stir between each heating increment. Onceit is creamy with no residual chunks, pour into a mixing bowl.
Using an electric mixer, slowly mix melted butter into the chocolate.
Stir in warm sugar-coffee mixture.
Beat together your eggs and egg whites in a separate bowl. Slowly pour them into your main batter and stir until completely combined.
Pour batter into the prepared springform pan and place on the middle rack your preheated oven. Fill a heatproof 9 x 13 pan with boiling (or nearly boiling) water and place it on the lower rack of your oven, directly beneath the cake.
Bake for 45-50 minutes. The cake will still appear slightly wet, but this is okay!
Allow the cake to cool to room temperature, then place in the refrigerator overnight before serving.