1. Place celery, onion, zucchini, tomatoes, bay leaf, oregano, basil, water and bouillon in slow cooker.
2. Cover and cook on LOW for 5-7 hours, or until vegetables are tender.
3. About 30 minutes before serving prepare a roux. Melt butter over low heat in a skillet and add in about half the flour. Stir constantly with a whisk for 2-3 minutes. Slowly stir in 1 cup hot soup. Whisk and slowly add in the rest of the flour. Add another 3 cups and stir until smooth. Add all back into the slow cooker. (If you want, you can use an immersion blender to make everything smooth and creamy)
4. Stir and add the Parmesan cheese, warmed milk, salt and pepper. Add additional basil and oregano if needed (the slow cooker does a number on spices and they get bland over time, so don’t be afraid to always season to taste at the end).
4. Cover and cook on LOW for another 30 minutes or so until ready to serve.
