5 tablespoons unsalted butter

1 medium onion, thinly sliced
2 medium apples, thinly sliced
1 large white potato, diced
1 1/2 cups chopped peeled butternut squash, fresh or frozen
Kosher salt and freshly ground pepper
1/2 teaspoon dried sage
2 tablespoons all-purpose flour
1/3 cup apple cider
4 cups chicken broth
1 cup milk
2 ounces thinly sliced prosciutto, torn into bite-size pieces
2 cups grated sharp cheddar cheese, plus more for garnish
Chopped chives, for garnish (optional)
Crusty bread, for serving (optional)

Melt 4 tablespoons butter in a large pot over medium-low heat, and add the onion, apples, potato and squash. Season with salt and pepper, and cook until the onion is soft, about 8 minutes. Stir in the sage and flour. Add the cider, and cook over high heat, stirring, until thickened. Add the broth and milk, cover, and bring to a boil; reduce to a simmer and cook, stirring, until the potato is soft, 8 to 10 minutes.

Meanwhile, heat the remaining 1 tablespoon butter in a large skillet over medium-high heat. Add the proscuitto, and cook until crisp, turning occasionally, about 2 minutes. Drain on paper towels. Add the cheese to the soup, and stir over medium-low heat until melted. Puree in a blender in batches until smooth; season with salt and pepper. Garnish with prosciutto, more cheese and chives, if using. Serve with bread if desired.