Add butter, onion, garlic, salt, pepper and red pepper flakes and cook until onions are translucent, about 3-4 minutes. Add tomatoes, vegetable broth and water and bring to a boil. Reduce heat and simmer for 10 minutes. Stir in the cannellini beans and spinach leaves and simmer until spinach leaves are wilted, about 1-2 minutes. Add the cream and the tortellini and simmer for an additional 3-5 minutes or until the pasta is just tender. Ladle into bowls. Garnish with parmesan cheese.