01 - Preheat oven to 400°F. Line a baking sheet with parchment paper.
02 - Place halved tomatoes cut side up on the prepared baking sheet. Drizzle with 1 tablespoon olive oil and season with salt and black pepper.
03 - Cut the top off the garlic head to expose the cloves. Drizzle with 1 tablespoon olive oil and wrap tightly in aluminum foil. Place garlic alongside tomatoes on the baking sheet.
04 - Roast in oven for 30 to 35 minutes until tomatoes are caramelized and garlic cloves are soft. Remove from oven and let cool slightly.
05 - In a large pot, heat 1 tablespoon olive oil over medium heat. Add chopped onion and sauté for 5 minutes until softened.
06 - Squeeze roasted garlic cloves from skins into the pot. Add roasted tomatoes with juices, broth, basil leaves, and optional red pepper flakes.
07 - Use an immersion blender to purée the mixture directly in the pot, or transfer to a stand blender in batches until velvety smooth.
08 - Return blended soup to the pot if needed. Stir in heavy cream and simmer gently for 5 to 10 minutes to blend flavors. Adjust seasoning as necessary.
09 - Ladle soup into bowls and garnish with fresh basil leaves, a swirl of cream, or crispy roasted tomato pieces as desired.