In a saucepan, melt the butter over medium heat. Add the chopped onion and sauté until translucent, about 5 minutes.

Add the minced garlic and cook for an additional minute until fragrant.

Stir in the crushed tomatoes and vegetable broth. Bring to a simmer and cook for 20 minutes.

Add the chopped basil, salt, pepper, and sugar (if using).

Use an immersion blender to puree the soup until smooth. Alternatively, carefully transfer to a blender in batches.

Stir in the heavy cream and heat through before serving.