Heat a large pot over medium heat, adding the butter or oil. Once melted, toss in the chopped onion and sauté until soft, about 5-7 minutes.

Season the onions with the salt, black pepper, red pepper flakes, dried oregano, and dried basil, stirring everything together for about a minute.

Stir in the minced garlic, cooking it for about 1 minute until fragrant. Add the whole tomatoes and diced tomatoes (including the juice from both cans).

Pour in the chicken broth, turn the heat to high, and bring the soup to a boil. Lower the heat to a simmer and let it cook for at least 10 minutes.

Turn off the heat and carefully blend the soup using an immersion blender until smooth. Alternatively, transfer the soup in batches to a regular blender.

After blending, return the soup to the pot. Stir in the cream slowly, adjusting the amount based on your preferred creaminess.

If desired, add the fresh chopped basil or use it as a garnish. Serve the soup warm.