In a 5 1/2-quart Dutch oven over medium-high heat, melt 1 Tbs. of the butter. Add enough pear slices to form a single layer and cook, turning once, until caramelized on both sides, 4 to 5 minutes total. Transfer to a plate.
In the same pot over medium heat, melt the remaining 2 Tbs. butter. Add the celery and onions and cook, stirring occasionally, until softened, about 10 minutes. Add the garlic and cook for 30 seconds. Stir in the butternut squash puree, the 4 cups broth, thyme, half of the pears or nectarines, salt and pepper. Bring to a boil, reduce the heat to medium-low and simmer for 10 minutes.
Using a blender, puree the soup in batches until smooth. Return the soup to the pot and stir in the half-and-half. Add more broth if needed to reach the desired consistency. Ladle the soup into bowls. Garnish with the prosciutto/bacon, remaining pear slices, hazelnut cream, yogurt or seeds. Serve immediately.
Toppings: Set out the various toppings and let your guests choose which they would prefer. The pears and hazelnut cream make for a more sweet soup, while the bacon, cumin yogurt or roasted butternut squash seeds make for a more savory bite.