1. In a large pot, heat olive oil over medium heat and sauté onion and garlic until translucent.
2. Add chopped tomatoes, salt, and pepper. Stir occasionally, cooking for about 15 minutes until tomatoes break down.
3. Stir in vegetable broth and bring to a simmer. Cook for another 10 minutes.
4. Using a blender or immersion blender, blend the soup until smooth.
5. Stir in heavy cream and fresh basil, then reduce heat and let simmer for 5 minutes.
6. While the soup simmers, prepare the garlic toast. Preheat the oven to broil.
7. In a small bowl, mix butter and garlic powder. Spread evenly on each slice of bread.
8. Top with shredded mozzarella cheese and place on a baking sheet.
9. Broil until cheese is melted and bread is golden, about 2-3 minutes.
10. Serve the soup hot with garlic toast on the side.