1Adjust oven rack to middle position, and heat oven to 450 degrees.
2Heat oil or butter in a heavy-bottom Dutch oven or large ovenproof saucepan over medium-high heat. Add onion and prosciutto or ham; saute until tender, 4 to 5 minutes.
3Stir in rice (can be removed from heat and covered for up to 2 hours in advance), then add wine, and simmer until the liquid has almost evaporated. Turn off heat. Add broth and water. Cover the pot with a sheet of heavy-duty foil, pressing the foil down so it's concave and rests on the broth. Place a lid over the pot to ensure an even tighter seal.
4Set pot in oven; cook for 25 minutes. Remove from oven. Use a potholder to remove lid and foil. Remembering that the handles are hot, set pot on low heat.
5Stir mixture, adding water if necessary, until rice is cooked and a little chewy at the center, the liquid is creamy, and the flavors of the new ingredients have melded in, about 5 minutes. Stir in 1 cup of Parmesan cheese, peas and/or parsley. Adjust seasonings, including salt and pepper, to taste.
6Spoon into shallow soup plates, sprinkling each serving with shaved Parmesan.
3 tablespoons olive oil or butter
1 small onion, cut into small dice
2 ounces prosciutto or 4 ounces ham, cut into small dice