In a large pot on med-low heat, add oil and butter.
One it melts, add the onion and sauté for about 15 min (mixing it around to keep from burning) or until perfectly caramelized.
Add in tomato paste and sauté together for another minute.
Stir in the crushed tomatoes and put the lid on the pot to bring to a gentle boil. After the soup has reached a gentle boil, turn to low heat. At this point, go ahead and make the grilled cheese sandwiches because the soup is almost done. A couple minutes before serving the dish, stir in the basil and cream to the soup.
Grilled Cheese Sandwiches
Place griddle/nonstick pan on med-low heat.
Generously butter one side of each of the sourdough bread slices.
Add a hefty handful of cheese to each slice and top with the other slice (butter side UP).
Remove from heat, slice, and serve with tomato basil soup---and enjoy!