A gammon joint is a British-style hammock joint that has been cured like bacon with the hog carcass -- unlike ham, which is cut from a hog before curing. It can be slightly saltier than ham, but you can prepare it in the oven just like a regular holiday ham. In Great Britain, whole gammon joints typically come with the skin still attached, so you'll have to remove it before serving. Cooking a smoked gammon joint is no different than roasting a traditional uncooked ham in the oven.
Submerge the whole gammon joint in a large container of water and place it in the refrigerator overnight. Soaking the gammon helps to remove any excess salt from the curing process.
Preheat the oven to 325 degrees Fahrenheit. Drain the water from the gammon joint and place it in a roasting pan. Cover the pan completely with foil.
Create a glaze for your gammon, if you so choose. One basic glaze that works well with ham or gammon consists of equal parts of brown sugar and honey, heated on the stove so that it's loose. You can also add a little mustard, another complementary flavor for ham. Set the glaze aside until you are ready to use it.
Place the covered gammon in the preheated oven to bake for about 20 to 30 minutes per pound. Remove it from the oven in the last 30 minutes of cooking to glaze the gammon. If your gammon came with the skin still on, slip a sharp chef's knife underneath the skin on one side and slice, peeling it away with your free hand. Use heat-proof kitchen gloves, and leave as much fat, which is directly underneath the skin, on the gammon as possible.
Score the fat on one side of the gammon, using crossing parallel lines to create diamond shapes. Brush the glaze generously over the scored fat as well as the rest of the gammon. Scoring allows the glaze to penetrate into the meat and makes for an attractive presentation.
Return the gammon to the oven, uncovered, to finish cooking, allowing the glaze to create a slightly crunchy crust. The gammon must be cooked to at least 145 degrees Fahrenheit for safe consumption. Remove the gammon from the oven and let it sit for 10 to 15 minutes before slicing and serving.