2 (14 oz) cans diced tomatoes, with juice
1 cup finely diced celery
1 cup finely diced carrots
4 cups chicken broth
1 cup finely diced onions
1/2 bay leaf
1 teaspoon dried oregano or 1 tablespoon fresh oregano
1 tablespoon dried basil or 1/4 cup fresh basil
1/2 cup butter
1/2 cup featherlight flour
1/8 teaspoon xanthan gum
1 cup Parmesan cheese
2 cups half and half, warmed
1 teaspoon salt
1/4 teaspoon pepper
In a large slow cooker, combine tomatoes, celery, carrots, chicken broth, onions, and bay leaf. (If you're using fresh basil and oregano, add them now also.) Cover and cook on low for 5 to 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 feather flour and xanthan gum; stir constantly with a whisk for 1 - 2 minutes. Slowly stir in 2 cups hot soup from the slow cooker. Stir until smooth.
Add it all back into the slow cooker. Stir and add Parmesan cheese, warmed half and half, salt, and pepper. Cover and cook on low for another hour until ready to serve.