Heat olive oil in a Dutch oven over medium heat. Add onions and celery, and sweat until onions are translucent, about 6 minutes. Add garlic and cook another 2 minutes. Add chicken stock, tomatoes and basil. Bring to a boil and reduce to simmer. Simmer soup until tomatoes are cooked down and flavors are combined, about 10 minutes. Blend soup with an immersion blender. Season to taste and serve topped with a balsamic drizzle.