When one does the "40 min. simmer, should the soup be covered or uncovered?

If the pot lid forms a very tight seal then leave it a big ajar on the pot.

A 40 minute simmer is a slow one. You need to turn the heat down far enough that you only see an occasional bubble rise to the surface. A brisk simmer for 40 minutes, with a tight lid, will give the dish a pressure cooker taste.

I often do the half-cover (half on, half off). Enjoy!