To a large saucepan, combine the Parmesan rinds, carrots, celery, garlic, onions, oregano, thyme, bay leaf and salt.
Add 8 cups broth and bring to a simmer over medium heat.
Simmer the broth for 1 hour 15 minutes, adjusting the heat to maintain a simmer and stirring occasionally to prevent sticking. (I simmered 6 hours)
Turn off the heat and allow the broth to cool slightly
Once cooled, strain Brodo, removing all solids. Place in containers. You can refrigerate or freeze until needed.