01 - Preheat the oven to 400°F (200°C).
02 - Cut the top off the garlic head to expose the cloves, drizzle with 1 tsp olive oil, wrap in foil, and place on a baking sheet.
03 - Place tomatoes (cut side up) and onions on the baking sheet, drizzle with remaining olive oil, and season with salt and pepper.
04 - Roast for 30 to 35 minutes until tomatoes are soft and caramelized and garlic is golden.
05 - Toss bread cubes with olive oil, oregano, and salt. Spread on a separate baking sheet and bake for 10 to 15 minutes, stirring once, until golden and crisp.
06 - Squeeze roasted garlic cloves out of their skins into a large pot.
07 - Add roasted tomatoes, onions, vegetable broth, basil, and sugar (if using) to the pot with garlic.
08 - Bring to a simmer over medium heat and cook for 10 minutes.
09 - Using an immersion blender or countertop blender in batches, purée the soup until smooth and return to the pot.
10 - Stir in cream if desired, then adjust seasoning with salt and pepper.
11 - Ladle soup into bowls, garnish with croutons and fresh basil.