1. Melt butter in a nonstick skillet over medium-high heat. Sauté onion and celery until tender, about 3 minutes.
2. Add flour and continue to cook, stirring, for 1 minute. Slowly pour in chicken broth and whisk until completely blended.
3. Empty crushed tomatoes into large pot.
4. Add contents of skillet along with basil, salt, and pepper. Bring to a boil, reduce heat, and simmer for 20 minutes.
5. Allow to cool and purée in blender to create a smooth texture. Reheat and serve.