Classic prosciutto is salt-cured ham; we use a similar curing method for duck breasts. Hang the duck from a rack in the refrigerator as it cures so air can circulate around it. For the tastiest results, do not trim the fat from the breasts. We tried this recipe with several brands of kosher salt and found Morton coarse kosher salt best preserved the duck's distinctive flavor. Serve with Parmigiano-Reggiano cheese and cantaloupe.