You probably won't get the bitter edge with lettuce as with escarole, and I don"t cook really tender greens in soups - just put in soup bowl and pour the finished soup over. Wilts w/o turning into overdone 'goo' (perfect description).

I've dealt with too much lettuce or not a salad favorite lettuce by treating it like other greens for soup. In deference to pierino's expertise, reduce the liquid so you can adjust when you see the results. Maybe it was just luck, but so far it's working.

As I can't translate your expletive I'll just say that escarole really does cook well in broth if that's your aim. You can substitute other lettuce except that they'll give up a lot of water and potentially turn into mushy goo. Try adding those at the very end, like the very, very end. End of story.

Doncha hate when that happens?

There are recipes in which lettuce is cooked, but I don't like any I've tried even though I love other cooked greens.