Preheat oven to 400°F (200°C). On a large baking sheet, combine the halved tomatoes, smashed garlic cloves, roughly chopped red onion, 3 tbsp olive oil, 1/2 tsp sea salt, and 1/4 tsp black pepper. Toss gently to coat everything. Spread in a single layer.

Roast for 30-35 minutes, or until the tomatoes are soft, slightly caramelized, and beginning to burst.

While the tomatoes are roasting, heat 1 tbsp olive oil in a large pot or Dutch oven over medium heat. Add the finely diced yellow onion, carrots, and celery. Sauté for 8-10 minutes, stirring occasionally, until the vegetables are softened and the onion is translucent.

Add the roasted tomato mixture (including all juices from the baking sheet) to the pot with the sautéed aromatics. Pour in the vegetable broth. Bring the mixture to a gentle simmer, then reduce heat to low, cover, and cook for 15 minutes, allowing the flavors to meld.

Remove the pot from the heat. Using an immersion blender, carefully blend the soup directly in the pot until it reaches your desired consistency – smooth or slightly chunky. Alternatively, transfer the soup in batches to a standing blender and blend until smooth. Be cautious when blending hot liquids.

Return the soup to the stovetop over low heat. Stir in the heavy cream (or coconut milk) and the chopped fresh basil. Add the optional 1 tsp sugar to balance acidity if needed. Season with additional salt and black pepper to taste. Heat through gently for 2-3 minutes, but do not boil after adding cream.

Ladle the creamy roasted tomato basil soup into bowls. Garnish with extra fresh basil leaves, a swirl of cream, or a drizzle of olive oil, and serve hot with crusty bread or grilled cheese.