Put a large stock pot over a medium flame and heat the oil. Add the prosciutto in batches and sauté until crisp. Remove to a paper towel lined plate. Set aside.
Add the shallots, red pepper flakes, sage and rosemary to the pot. Cook until the shallots have softened, about 5-7 minutes.
Add the passata, Salt and water to the pot. Cook for 5 minutes and then add the butternut squash and potatoes.
Add the chicken broth to the pot making sure the squash and potatoes are totally covered. If they aren’t, add enough water to the pot to cover.
Bring to a boil, cover and simmer until the squash and potatoes are tender, about 30-40 minutes.
Using an immersion blender, blend the soup until smooth. Serve in warm bowls topped with the crispy prosciutto.