Bake potatoes in oven at 400 degrees for 1 hour to 1 hour 15 minutes until soft.
As soon as potatoes are baked, cut in half with serrated knife then scoop the insides out and put into a large bowl, leaving a small amount of potato around in the skin to maintain the structure.
Mix hot potatoes with butter, Boursin cheese, salt, and 1/2 cup shredded parmesan cheese using a hand mixer or mix by hand.
Spoon mixture back into potato skins filling to just above the top of the skin. Top with remaining parmesan cheese and put back on baking sheet.
Bake for an additional 20-25 minutes at 400 degrees, until the top of the potato mixture is beginning to brown.
Remove from oven and top with crispy prosciutto pieces. Serve hot or at room temperature.
Notes
To crisp the prosciutto, line baking sheet with parchment paper and lay prosciutto flat. Bake in the oven at 400 degrees for 10-15 minutes or until crisp.