This is really good soup! I made it per the directions but I don't eat beef, so used an equal mix of chicken and vege-table stocks.
This soup tastes a lot like what you might order at a nicer restaurant. I do question the use of mozzerella and asiago cheeses - two Italian cheeses - in something that is so decidedly French. I personally was not a fan of the resulting taste and next time I will combine parts of this and my recipe, which calls for the use of Gruyere or true Emmental swiss (no substitutions). If desired, throw into the soup the rind of one hard French or Swiss-made cheese of your choice, doing so after removing kettle from flame to rest (about ten minutes). I also use sherry wine, not balsamic vinegar, because my grandmother always used this flavor in soups and casseroles. The sherry imparts a subtle sweet-smokey flavor that is a nice counterpoint to the Gruyere's mild tanginess. Remove cheese rind, and ladle the soup into bowls. Top with a 1/2 in. slice of dense, day-old, crusty french baguette that has been lightly toasted beforehand. Top with Gruyere swiss or Emmental and continue with recipe, broiling as directed. I found just 3 minutes in the broiler was enough. Keep an eye out for over cooking - there is nothing worse than the taste and smell of burnt cheese.