1 (11- to 13-lb) bone-in smoked pork shoulder (sometimes called picnic ham)
2 medium leeks, chopped
1 large onion, chopped
3 medium carrots, cut into 1/2-inch cubes
2 celery ribs, cut into 1/2-inch cubes
2 garlic cloves, finely chopped
6 (5-inch) fresh thyme sprigs plus 2 tablespoons finely chopped leaves
6 fresh flat-leaf parsley stems plus 1/4 cup finely chopped leaves
2 tablespoon nutmeg, 1 teaspoon whole black peppercorns
4 whole cloves
5 tablespoons unsalted butter, softened
2 cups dry white wine
4 cups water
1/3 cup all-purpose flour
Put ham in deep 10- to 20-quart pot and cover with cold water (don't worry if bone sticks out). Bring to a boil, and then drain ham.
Put oven rack in lower third of oven (remove any other racks) and preheat oven to 350°F.
Wash leeks in a bowl of cold water, then lift out and drain well. Cook leeks, onion, carrots, celery, garlic, thyme sprigs, parsley stems, nutmeg, peppercorns, and cloves in 2 tablespoons butter in wide 7- to 10-quart heavy pot (see "special equipment," above) over moderately high heat, stirring occasionally, until vegetables are softened and beginning to brown, about 10 minutes. Add wine and bring to a boil, then add ham, skin side down, and water (liquid will not cover ham) and return to a boil.
Cover pot tightly with lid or, if ham sticks up over top of pot, with heavy-duty foil. Braise ham in oven 1 hour.
Turn ham skin side up and continue to braise in oven, covered, until thermometer inserted into center of ham (do not touch bone) registers 120°F, about 1 hour more (if ham was labeled "fully cooked"), or 160°F, about 2 hours more (if ham was labeled "partially cooked").
While ham braises, mash together flour and remaining 3 tablespoons butter with a fork to make a Beurre manié.
Transfer ham to a platter and let stand, loosely covered with foil, 45 minutes.
While ham stands, pour braising liquid through a fine-mesh sieve into a 3-quart saucepan, pressing on and discarding solids, and skim off any fat. Bring braising liquid to a simmer and whisk in Beurre manié 1/2 tablespoon at a time (sauce will become lumpy). Continue to simmer, whisking, until sauce is smooth and slightly thickened, about 5 minutes. Remove from heat and stir in chopped thyme and parsley.
Remove skin from ham, then slice meat and serve with sauce.