In a large Dutch oven, combine olive oil and butter. Heat over medium heat until the butter is melted. Add the onion. Cook, stirring frequently, until softened, about 8 minutes. Stir in the garlic and cook for another 5 minutes or until very fragrant and just starting to brown.

Add the tomatoes. Swirl the cans with some of the chicken stock to get the rest of the tomato juices and pour into the pot with the remaining stock. Stir in the sugar and black pepper.

Bring to a boil (this will take about 10 minutes), then reduce the heat to medium-low and continue simmering for 30 minutes, stirring occasionally. Remove from the heat.

Using an immersion blender, pulse the soup to break up the tomatoes a bit or until your desired consistency. (I do not recommend transferring the soup to a high-speed blender as blending olive oil can turn it very bitter. Mash with a potato masher to break up the tomatoes a bit if you don’t have an immersion blender.) Taste and add salt, if needed. Stir in the cream. Serve immediately topped with fresh basil.