Heat olive oil in a large pot over medium heat.
Add diced onions and sauté until translucent.
Stir in minced garlic and cook for another minute.
Add chopped tomatoes and cook until they soften.
Pour in the vegetable broth and bring to a boil.
Reduce heat and simmer for 20 minutes.
Blend the soup with an immersion blender until smooth.
Stir in sugar, salt, and pepper to taste.
If desired, add heavy cream for a richer flavor.
Serve hot, garnished with fresh basil leaves.