Step 1

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.

Step 2

Meanwhile, heat the remaining 1 tablespoon butter in a large skillet over medium-high heat. Add the prosciutto and cook until crisp, turning occasionally, about 2 minutes. Drain on paper towels.

Step 3

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 the prosciutto, more cheese and chives, if using. Serve with bread, if desired.