Pat the duck breast dry and cover the bottom of the pan in a layer of salt. Nestle in the duck breast skin-side up and bury it in salt. Ensure that the duck isn't touching anything other than salt.
Refrigerate covered for 24-hours*.
The next day, rinse the duck breast under cold water, washing off the salt. Pat dry.
Season both sides of the duck breast with white pepper.*
Wrap the duck in a length of cheesecloth and tie it up with kitchen string.
Hang the duck up to dry cure in a cool, humid place. A basement or cold room work beautifully for this, the ideal temperature being 50-60ºF/8-15ºC.
After a week, squeeze the middle of the duck to check for doneness. If it feels squishy (raw), let it hang for another day or two to firm up.
When ready to serve, thinly slice the prosciutto on the bias, ensuring that each piece comes with a layer of fat.