**Roast the Tomatoes:** Preheat your oven to 400°F (200°C). Arrange the halved tomatoes and garlic cloves on a baking sheet. Drizzle with olive oil and sprinkle with salt and pepper. Roast for 25–30 minutes until the tomatoes are tender and slightly caramelized.

**Sauté the Onion:** In a large soup pot, heat 1 tablespoon of olive oil over medium heat. Add the diced onion and cook until softened, about 5 minutes.

**Blend the Tomatoes:** Transfer the roasted tomatoes, garlic, and any juices from the baking sheet into a blender. Blend until smooth. Alternatively, add them to the pot and use an immersion blender.

**Combine Ingredients:** Add the tomato puree to the pot with the sautéed onion. Pour in the vegetable broth, and stir in the dried thyme. Simmer for 10–15 minutes to let the flavors meld.

**Add Basil and Cream:** Stir in the chopped basil and heavy cream, if using. Cook for an additional 2 minutes. Taste and adjust seasoning with salt and pepper if needed.

**Serve:** Ladle the soup into bowls, garnish with grated Parmesan cheese or additional basil leaves, and serve hot.