Heat olive oil in a large pot over medium heat.
Add diced onion and sauté until translucent.
Stir in minced garlic and cook for an additional minute.
Add the chopped tomatoes and cook until softened.
Sprinkle in the sugar, salt, and pepper.
Pour in the vegetable broth and bring to a boil.
Reduce heat and let simmer for 20 minutes.
Use an immersion blender to puree the soup until smooth.
Adjust seasoning to taste.
Serve hot, garnished with fresh basil and croutons.