Preheat the oven to 400°F (200°C).

On a baking sheet, toss the halved tomatoes, quartered onion, and unpeeled garlic cloves with olive oil, salt, and pepper.

Spread them out in a single layer and roast for 30-35 minutes until caramelized and tender.

Once roasted, let the vegetables cool slightly, then squeeze the garlic out of its skin.

In a blender, combine the roasted vegetables, fresh basil, vegetable broth, and balsamic vinegar.

Blend until smooth and creamy, adjusting the consistency with more broth if necessary.

Pour the blended soup into a saucepan and heat over medium heat until warmed through.

Taste and adjust seasoning with additional salt and pepper if needed.

Ladle the soup into bowls and garnish with extra basil leaves if desired.

Serve hot with crusty bread.