While an important ingredient in the American Southeast, folks in much of North America are not particularly familiar with Hog Jowels. Basically, it's the pig's cheeks. While the Italian Guanciale is salt cured with herbs, Hog Jowl in the US is generally salt cured and smoked like bacon.
In American Southern cuisine, Hog Jowl is used much like bacon. it can be sliced and fried like bacon, and is often used as a flavoring ingredient with beans and greens. The larger of the photo specimens was 6-3/4 inches long, 2 inches thick and 2-1/2 inches at its widest.
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Buying: Here in Los Angeles, I find it most often at the Altadena location of Super King Markets. This store's customers include a fairly high black population (20% to 25%), some of whom would know what to do with this ingredient. It is rather difficult to find anywhere else. Of course, in the US Southeast it is much more common.
Storage: Stored tightly sealed in the refrigerator it should last for a couple of weeks. If it gets a few spots of mold on it, just scrape the mold off before slicing.
Prep: Basically, just cut it into the desired pieces. Properly, it will include the skin. If you are just going to fry it, cut the skin off (and reserve for another use) as it will be quite tough. If it will be simmered for some time, leave the skin on.
Cooking: Use as per recipe - or as a substitute for ham hocks or bacon. Note that jowls have a lot more fat than regular bacon, and that fat renders rather easily, so you may need to pour some off.
Subst: Smoked Bacon, Smoked ham hocks, .