Preheat your oven to 400°F (200°C).
Halve the Roma tomatoes and remove the seeds. Peel and chop the onion and red bell peppers into large pieces. Chop the top off of the garlic heads.
Spread the seasoned vegetables in a single layer on a baking sheet lined with parchment paper or aluminum foil. Drizzle the olive oil and balsamic vinegar over the vegetables, then sprinkle with salt, black pepper, and Italian seasoning. Toss well to coat all the vegetables evenly with the oil and seasonings.
Roast the vegetables in the preheated oven for 30-35 minutes or until they are soft and slightly charred.
Remove the roasted vegetables from the oven and transfer them to a blender or food processor. Blend the vegetables until you achieve a smooth consistency. If needed, do this in batches. Pour the blended mixture into a large pot on the stove.
Place the pot with the blended mixture over medium heat. Add the vegetable broth to the pot and stir well to combine. Bring the mixture to a light simmer and let it cook for about 10-15 minutes, stirring occasionally.
Now, add the sugar, garlic powder, onion powder, salt, and pepper to the soup. Adjust the seasonings according to your taste preferences. Stir in the milk of your choice to achieve a creamy consistency. Let the soup simmer for an additional 5 minutes.
Ladle the roasted tomato soup into individual serving bowls. Garnish each bowl with fresh basil leaves. Optionally, serve the soup with grilled cheese sandwiches on the side. Enjoy! :)