- In a large pot, heat the butter and olive oil over medium heat. 
- Add the diced onion and minced garlic. 
- Cook until they are soft and translucent, about 5 minutes. 
- Pour in the canned tomatoes and chicken broth. 
- Stir well and bring to a simmer. 
- Let the mixture cook for about 15 minutes so the flavors meld together. 
- Use an immersion blender to puree the soup until smooth. 
- Alternatively, transfer it in batches to a countertop blender. 
- Stir in the sugar, heavy cream, and sherry (if using). 
- Season with salt and pepper to taste. 
- Continue to simmer for another 10 minutes. 
- Serve the soup warm with your choice of croutons or a side of bread.