Well Kosher I can only use Swiss since i can't really find gruyere kosher.
UPDATE: I made it last week for Valentine's day for my wife and she loved it! I ate it once at a place called Lefty's in upstate ny(before i knew there was beef broth in it) and the taste was 1:1 the same. I cooked the 2.5 lbs onions for a hour and 15 min. then added 3 cubes of the beef cubes to 6 cups of water, boiled it. to the onions i added paprika bay leaf and black pepper. I added the liquid , reserved some mixed with wondra, added that then let it sit half covered over low fire for 45 mins(as was 920 already).
In the end i added the italian bread/some swiss , oven to broil and it came out Great! i can post some pictures as well if i can figure out how to.
The only change i would do is cut the onions after thin mandolining in 1/2 so that they werent so big in the soup?
Question: I was correct to leave the pot 1/2 covered right, so the soup didnt evaporate, it has nothing to do with the onions dispersing or not.