1. In a large soup pot over medium high heat add the oil and butter. Once the butter is melted and bubbling add the onions, sweet potato, carrots, and bell pepper. Sauté until soft and lightly golden, about 8-10 minutes. 

2. Add the tomato paste and garlic. Mix to combine and allow the tomato paste to caramelize and darken in color, about 2-3 minutes. 

3. Add the balsamic vinegar, crushed tomatoes, stock, heavy cream, Italian seasoning, salt and pepper. Stir to combine. Bring to a boil and then turn the heat to low and simmer for 25-30 minutes. 

4. In a large blender, carefully add 1/3 of the soup along with 1/2 cup grated Parmesan and 1/2 cup Crème Fraîche (or sour cream). I do this in three batches. Make sure the lid to the blender is slightly ajar or remove the vent cover on the lid and place a cloth over the lid, blend until smooth. (The soup is very hot at this point and you do not want to trap the steam in the blender or it will explode, so make sure the steam has a way to vent out of the lid). Once the soup is blended, pour into a bowl and do the remaining batches of soup. Do this until all the soup is blended.

5. Return blended soup to the soup pot. Taste and add any additional salt or pepper. 

6. For the grilled cheese croutons, cube half a baguette. Place the cubes on a baking sheet lined with parchment paper. Drizzle the cubes with olive oil and toss. Broil for 2-3 minutes or until golden brown. 

7. Ladle tomato soup into oven safe bowls. Add some croutons to each bowl. Sprinkle with freshly shredded sharp cheddar cheese. Place the bowls on a baking sheet lined with parchment paper. Broil until the cheese is melty, about 3-5 minutes.