Brothy Tomato and Bean Soup

A couple of weeks ago we had chicken salad sandwiches from a leftover roast for dinner and I wanted a light soup to complement them.  A can of tomatoes, chicken broth and Great Northern beans and an adaptation of Marcella 
 Hazan's Tomato Sauce with Onion and Butter laid the the groundwork for this.

For the tomato sauce:
1   14.5 ounce can plum tomatoes, crushed
3 Tbl butter
1/2 cup roughly chopped onion
1 garlic clove, halved
1 cup water
1/4 tsp salt

Place all ingredients in a medium sauce pan and simmer for 20 to 30 minutes until thick.  Set aside.

For the soup:
1/2 pound Great Northern beans which have been soaked overnight and the cooked for about 45 minutes until done.
1 cup of the bean broth, reserved from the cooked beans
4  1/2 cups chicken broth
1 large sprig fresh thyme
Salt and pepper to taste

Place the chicken broth and thyme sprig in a medium soup pot and simmer for about 8 minutes.
Meanwhile place the tomato sauce, 1/2 cup bean broth, and 1/2 cup cooked beans in a bowl or blender and blend until smooth.  If using a bowl, blend with an immersion blender.
Remove the thyme sprig from the broth, add the tomato mixture, the remaining bean broth and the beans.  Simmer for another few minutes and season to taste with salt and pepper.