Step 1: Preheat the Oven - Begin by preheating your oven to 375°F (190°C).

Step 2: Prepare the Tomatoes - Slice the Roma tomatoes in half lengthwise, lay cut side up on a baking sheet, drizzle with olive oil, and sprinkle with salt and pepper.

Step 3: Roast the Tomatoes - Roast the tomatoes for about 1 hour, or until tender and slightly charred.

Step 4: Sauté the Aromatics - In a pot, heat olive oil or butter, then add chopped onion and sauté for 5 minutes. Add garlic and thyme, cook for 1 minute until fragrant.

Step 5: Combine Ingredients - Stir in crushed San Marzano tomatoes and fresh basil, add sugar if desired, and simmer for 10 minutes.

Step 6: Add Roasted Tomatoes and Stock - Stir in the roasted tomatoes with juices and stock, simmer for another 30 minutes.

Step 7: Blend the Soup - Blend the soup until you reach your desired texture, using an immersion blender or traditional blender in batches.

Step 8: Finish and Serve - Stir in heavy cream, adjust seasoning, and serve hot garnished with fresh basil leaves and croutons.