Preheat your oven to 400°F (200°C).
Wash and slice the fresh tomatoes in half. Lay them cut-side up on a baking sheet and drizzle with olive oil, salt, and pepper.
Bake the tomatoes for 25-30 minutes until they are caramelized and bursting with flavor.
In a large pot, heat some olive oil over medium heat. Add chopped onions and sauté until translucent, about 5 minutes. Then add minced garlic and cook for an additional minute.
Add the roasted tomatoes to the pot along with any juices. Pour in the vegetable broth and bring to a boil.
Reduce heat and let it simmer for about 15-20 minutes to blend the flavors.
Use an immersion blender to puree the soup until smooth.
Stir in fresh basil leaves and let it cook for a few more minutes.
Taste and adjust seasoning if needed. Serve hot.