Tomato Basil Parmesan Soup

pic from 365 days of slowcooking...which is where recipe is from

2 (14 oz) cans diced tomatoes, with juice
1 cup finely diced celery
1 cup finely diced carrots
1 cup finely diced onions
1 tsp dried oregano or 1 T fresh oregano
1 T dried basil or 1/4 cup fresh basil
4 cups chicken broth
½ bay leaf
½ cup flour
1 cup Parmesan cheese
½ cup butter
2 cups half and half, warmed
1 tsp salt
¼ tsp black pepper

Add tomatoes, celery, carrots, chicken broth, onions, oregano, basil (if using fresh oregano and basil add it now, if using dried oregano and basil add it in the last hour of cooktime), and bay leaf to a large slow cooker. Cover and cook on LOW for 5-7 hours, until flavors are blended and vegetables are soft. About an hour before serving prepare a roux. Melt butter over low heat in a skillet and add flour. Stir constantly with a whisk for 5-7 minutes. Slowly stir in 1 cup hot soup. Add another 3 cups and stir until smooth. Add all back into the slow cooker. Stir and add the Parmesan cheese, warmed half and half, salt and pepper. Cover and cook on LOW for another hour until ready to serve.