Step 1: Heat 2 tablespoons of olive oil in a large pot or Dutch oven over medium heat. Add 1 chopped yellow onion and 2 cloves of minced garlic. Sauté until softened and fragrant, about 5-7 minutes.
Step 2: Pour in two 28-ounce cans of high-quality diced tomatoes (preferably San Marzano), along with their juices. Add 4 cups of vegetable broth, 1 teaspoon of dried oregano, 1/2 teaspoon of sugar, and a good pinch of salt and black pepper. Stir everything together.
Step 3: Bring the mixture to a gentle simmer. Reduce the heat to low, cover, and let it cook for about 10-15 minutes, allowing the flavors to meld.
Step 4: Carefully transfer the soup in batches to a blender, or use an immersion blender directly in the pot. Blend until completely smooth and creamy. If using a standard blender, be sure to vent the lid to allow steam to escape.
Step 5: Stir in 1/2 cup of heavy cream and 1/2 cup of fresh basil leaves, roughly chopped. Heat gently for another 2-3 minutes, just until warmed through, but do not bring to a rolling boil after adding the cream. Taste and adjust seasonings as needed.