Cut the tomatoes into quarters. Slice off the top of each garlic bulb, exposing the cloves.
Place the tomatoes, onion, and garlic bulbs in a large baking pan. Sprinkle with Italian herbs, salt, and black pepper, then drizzle everything with olive oil.
Bake at 190°C (375°F) for about 40 minutes, or until the tomatoes and onions are nicely roasted and lightly golden around the edges.
Once roasted, squeeze the softened garlic cloves out of their papery skins. Discard the garlic skins, then transfer the roasted tomatoes, onion, garlic, and all the flavorful juices from the pan into a blender.
Add the heavy cream and fresh basil leaves. Blend until smooth and creamy. Taste and adjust with more salt or pepper if needed.
Pour the soup into bowls, drizzle with a little extra cream, and garnish with fresh basil leaves.
