Preheat your oven to 400°F (200°C). This will ensure even roasting of the vegetables.
On a large baking sheet, arrange the halved tomatoes with the cut side facing up, the quartered onion, and the unpeeled garlic cloves. Drizzle the olive oil generously over the vegetables, then season with sea salt and freshly ground black pepper.
Roast in the preheated oven for approximately 30-35 minutes, or until the tomatoes are tender and caramelized with a rich aroma.
Once roasted, remove the pan from the oven and allow the vegetables to cool slightly. After a few minutes, carefully squeeze the garlic cloves out of their skins, discarding the peels.
In a large pot, combine the roasted vegetables with the vegetable broth. If desired, add the teaspoon of sugar to balance the acidity of the tomatoes. Bring this mixture to a gentle boil over medium heat.
Once boiling, reduce the heat and let the soup simmer for 10-15 minutes.
Using an immersion blender, blend the soup until it reaches a velvety smooth consistency.
Stir in the freshly chopped basil leaves and the heavy cream if you're using it. Allow the soup to simmer for an additional 5 minutes on low heat.
Taste your soup and adjust the seasoning with additional sea salt and fresh pepper as needed.
Notes
For a delightful touch, garnish with olive oil, cream, and fresh basil. Pair with crusty artisan bread.