Melt the butter in a soup pot, saute the onion until soft. Add the tomatoes and the tomato paste. Cook, stirring often, over low heat for about 15 minutes. Add the water and the chicken broth and bring to a boil. Add the bread, garlic, basil, and salt. Simmer until the bread is saturated and falling apart. Puree with an immersion blender. Serve with olive oil and Parmesan.