Put basil, pine nuts, parmesan, garlic, and olive oil in a blender and blend to make pesto. You can also use 1 1/2 cups pre-made pesto.
Melt butter in stock pot and sauté onions and celery until softened (about 5 minutes).
Transfer onions, and celery, and pesto to a crock pot. Add tomatoes and juice, oregano, and sherry and cook on high for 4-6 hours.
Blend soup in batches in a blender or food processor until smooth - transfer to stock pot.
Add heavy cream and cook for 30 minutes. Garnish with parmesan cheese and serve hot.
You can substitute 1 1/2 cups of pre-made (Costco) basil pesto instead of making homemade. Soup can be made entirely in the stock pot instead of a crock pot - cut the cooking time down to 2 hours on a low simmer.