In a large stock pot, heat olive oil and butter. When butter is melted add onions, carrots, celery, and garlic

Saute for 2-3 minutes or until onion is tender. Add the squash.

Then add potato, sage, salt, red pepper, and chicken broth. Bring to a boil and then turn down to a simmer. Simmer with the lid on for 30-40 minutes or until everything is tender. Check a piece of squash and also a piece of celery and potato to make sure they area fork tender. Stir in brown sugar.

Use an immersion blender, or transfer soup to a regular blender and puree until smooth.

Topping:  Heat a medium sized heavy skillet to medium high heat.  Add a drizzle of olive oil and swirl to coat pan.  Add prosciutto and cook until crisp and browned.  Remove with slotted spoon and lay on paper towels to drain.  Add sage to pan and cook in prosciutto drippings (add a little extra olive oil if needed) until crisp.  Drain on paper towels as well and sprinkle with a little sea salt.  

To serve, ladle soup into bowls, top with a drizzle of cream and a sprinkle of prosciutto and sage leaves.