Heat olive oil in a large pot over medium heat.
Add diced onions and sauté until translucent (about 5 minutes).
Stir in the minced garlic and cook for another minute.
Add the chopped tomatoes, sugar, salt, and pepper. Cook for about 10 minutes until tomatoes soften.
Pour in the vegetable broth and bring to a boil.
Reduce heat and simmer for 15 minutes.
Use an immersion blender to puree the soup until smooth.
Stir in fresh basil and heavy cream if desired.
Taste and adjust seasoning before serving.