Preheat oven to 400°F. Place the halved Roma tomatoes, onion, and garlic on a large baking sheet. Drizzle with olive oil and toss to coat.Roast for 35–45 minutes until everything is soft and slightly caramelized. Add the roasted vegetables and all their juices to a large pot.
Pour in the broth and let it simmer for 10–15 minutes to bring everything together.
Use an immersion blender (or standard blender) until the soup is smooth and creamy.
Add salt, and pepper. Stir in fresh basil.
Roasting enhances sweetness, so adjust seasoning to your preference.