This recipe, courtesy of Nate Appleman, can be found in "A16 Food + Wine," and is used to make his Minestra Maritata.
Source: The Martha Stewart Show, February Winter 2009
Yield Makes 8 to 9 cups
8 ounces prosciutto, trimmings and ends plastic hooks and strings removed, coarsely chopped
Place prosciutto in a large pot with 12 cups water; bring to a boil over medium heat. Reduce heat to medium-low and simmer, skimming surface occasionally, until the fat from the prosciutto is rendered into the broth, about 2 hours.
Strain through a fine-mesh strainer into an airtight container; let cool. Cover and keep refrigerated for up to 1 week, or freeze for up to 3 months. Before using, bring broth to a simmer and stir to reincorporate fat.