Melt butter in large pot on medium heat. Add carrots, celery, onion, garlic, salt & pepper. Cook until soft, stirring often (about 8 minutes).
Sprinkle vegetables with flour and stir. Cook 3 minutes, stirring occasionally.
Whisk in canned tomatoes, sun-dried tomatoes, and chicken broth. Add bay leaf & thyme. Bring to boil, reduce to a simmer, and cover. Simmer for 30 minutes.
Remove from heat. Remove thyme & bay leaf. Carefully blend with an emersion blender or in a high-speed blender until smooth (and return to pot).
In a small bowl whisk together 1/3 cup sour cream and heavy cream. Add 1 cup of pureed soup to the sour cream/cream mixture in bowl. Stir to incorporate. Stir contents of bowl back into the pot of soup until combined.