Bring to a boil and then turn down to a simmer for roughly 20 - 25 minutes. (goodeatings.com)
Bring the soup to the boil and then turn down to simmer for approximately 30 minutes or until the vegetables are as soft as you prefer. (neilshealthymeals.com)
Turn down to a simmer on low for 35 - 45 minutes until thickened. (ciaprochef.com)