Preheat oven to 400°F (200°C).

Place tomatoes (cut side up), onion quarters, and garlic head on a baking sheet. Drizzle with olive oil and balsamic vinegar. Sprinkle with thyme, oregano, salt, and pepper.

Roast for 45 minutes, or until tomatoes are caramelized and garlic is soft.

Let cool slightly. Squeeze roasted garlic cloves out of their skins.

Transfer roasted vegetables to a large pot. Add broth and tomato paste.

Bring to a boil, then simmer for 10 minutes.

Use an immersion blender to puree the soup until smooth. If using a regular blender, blend in batches and return to the pot.

Stir in fresh basil and cream (if using). Simmer for 5 more minutes.

Taste and adjust seasoning with salt and pepper.

Serve hot, topped with croutons or grilled cheese cubes if desired.