Peel and cube the potatoes. Place the potatoes in a 3-quart saucepan; cover with water by 1 inch. Bring the potatoes to a boil and reduce heat. Simmer for 20 minutes or until fork tender. Drain and keep warm.
Meanwhile, in an 8-inch skillet, heat the oil over medium heat. Add the prosciutto. Cook for 8 to 10 minutes or until crisp, stirring frequently. Stir in the Italian seasoning and set aside.
Mash the potatoes with a hand masher or electric mixer.
Stir in the sour cream and milk; beat with a spoon until smooth. Stir in the prosciutto and Parmesan cheese. Season with the salt and pepper.