This "King of Mystery Meats" is made by several companies in or around Trenton, New Jersey. Maker John Taylor has become sufficiently dominant to make "Taylor Ham" a generic alternative to Jersey Pork Roll but some connoisseurs prefer products from smaller makers.
The recipes are all secret, but one thing is for sure, salt. Enough salt so I think the product is eternal - even mold doesn't grow on it. Several sellers ship pork roll to most points in the U.S. packed in styrofoam with frozen gel packs. The photo specimen (4 inch diameter, 3 pounds) was shipped to me UPS 4 day ground courtesy Mike Vitale (Yendor). The most famous use for Pork Roll is probably the Jersey Breakfast Sandwich (see Recipes).
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Buying: Unless you live in New Jersey or adjacent states this is a mail order item. Fortunately it's easily available (many people from New Jersey can't live without it). Shipping costs are not so astronomical as for most "gourmet" items because it can be shipped ground to most points in the U.S.. Typical vendors are Pork Roll Xpress (where mine came from), Jersey Boy Pork Roll, Jersey Pork Roll and BuyNJPorkRoll
Storage: Keep refrigerated. It has a liberal expiry, a couple months as I recall, but with good refrigeration I know from experience that expiry is not a hard date.
Cooking: Pork roll is most often fried, sliced for sandwiches or diced for hash, ham and eggs, or similar recipes. It is also used in baked recipes and in stuffings. If you slice it you need to deeply incise the edges as shown in the photo or the slices will bulge up badly in the middle and not fry evenly. Pork roll should not be over-fried or it will shrink badly and dry out.