Preheat your oven to 400°F (200°C).

Cut the tomatoes in half (if using large tomatoes) and place them on a baking sheet along with the garlic cloves and quartered onion.

Drizzle the olive oil over the tomatoes, garlic, and onion. Sprinkle with salt and black pepper.

Roast in the preheated oven for 35-40 minutes, or until the tomatoes are soft and slightly caramelized.

Remove the roasted vegetables from the oven and let them cool slightly.

Transfer the roasted tomatoes, garlic, and onion to a blender or food processor. Add the vegetable broth, fresh basil leaves, and balsamic vinegar.

Blend until smooth. If the soup is too thick, add more broth until you reach your desired consistency.

Pour the blended soup into a pot and heat over medium heat. If desired, stir in heavy cream for added richness.

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

Serve hot, garnished with fresh basil leaves if desired.