Heat the grapeseed oil in a pot over medium heat. Add the onions, carrots, celery and garlic, and sweat for 5 to 8 minutes. Add the thyme and saute for 1 to 2 minutes.
Add the whole tomatoes and tomato puree. Crush the tomatoes with a whisk as you stir the soup. Bring the soup up to a simmer, reduce the heat to medium-low and cook for 15 to 20 minutes.
Add the heavy cream and basil, and puree the soup using an immersion blender. Bring back up to a simmer and cook for another 5 to 10 minutes. Season with salt and pepper.