Add tomatoes, celery, carrots, broth, onions, oregano, basil and bay leaf to slow cooker.
Cover and cook on low 5-7 hours until flavors blended and veggies soft.
About 30' before serving prepare a roux. Melt butter over low heat in skillet and add flour. Stir constantly with a whisk 5 - 7 minutes. Slowly stir in 1 cup hot soup. Add another 3 cups and stir until smooth. Add all back into slow cooker.
Stir and add Parmesan cheese, warmed half and half, salt and pepper. Add basil and oregano if needed. Cover and cook on low another 30 minutes.
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