In a large saucepan, heat 2 tablespoons of butter over medium heat. Add 1 finely chopped onion and 2 minced garlic cloves, and sauté until the onion is translucent and soft.
Add 500 grams of chopped ripe tomatoes, 1 teaspoon of sugar, 1/2 teaspoon of salt, and 1/4 teaspoon of black pepper. Cook for 10 minutes, stirring occasionally.
Pour in 500 ml of vegetable stock and bring the mixture to a boil. Reduce the heat and let it simmer for 20 minutes.
Use an immersion blender or a regular blender to puree the soup until smooth. If using a regular blender, let the soup cool slightly before blending and blend in batches if necessary.
Return the soup to the saucepan and stir in 200 ml of fresh cream. Cook over low heat for 5 minutes, stirring occasionally.
Taste and adjust the seasoning if needed. Serve hot, garnished with fresh basil leaves or croutons.