Cut up ducks: Separate thigh-leg portions in one piece. Bone thigh, leaving it attached to leg bone. Cut off top inch of leg bone with a heavy cleaver. Trim all visible fat from thigh-leg pieces; reserve fat in a heavy saucepan. Remove duck breasts and reserve for another use. Cut away as much fat and skin from the carcass as possible, chop in small pieces, and add to reserved fat.
Marinate duck pieces: Sprinkle thigh-leg portions all over with salt and turn skin-side down. Sprinkle with mixed spices, saltpeter and pepper. Place herb sprig on each portion. Press together 2 pieces to make 3 packages of thigh-leg portions with skin on outside. Place in a nonreactive baking dish or roasting pan, cover tightly and marinate 24 hours, refrigerated.
Render duck fat: Add 1 1/2 cups of the wine and just enough water to saucepan of reserved fat to moisten. Heat pan over medium heat and simmer for about 1 hour, or until all wine and water has evaporated, and only golden duck fat remains. Strain out cooked skin and reserve fat.
Prepare confit: Preheat oven to 300 degrees. Remove duck thigh-leg pieces from refrigerator, discard herb sprigs and pat dry with paper towels. Brush lightly with rendered fat and broil in a preheated broiler, skin-side up, until skin browns, about 4 minutes. Remove from heat, sprinkle with the remaining 1/2 cup wine and let rest for several minutes. Meanwhile, heat rendered duck fat in a large, heavy casserole. When fat boils add duck pieces. Add enough additional rendered duck or goose fat to cover. Bake covered in 300 degree F oven, 2 hours, or until duck is extremely tender, but not falling apart. Place a rack or crisscross a pair of chopsticks in bottom of a heavy earthenware crock. Lay duck pieces on rack, then pour warm fat over to completely cover and seal pieces. When cool, cover top of crock and refrigerate at least 24 hours before serving. Duck will keep, refrigerated, for several weeks.
To finish: Preheat oven to 400 degrees. Remove duck pieces from crock and scrape off most of fat. Place in a roasting pan and heat in a 400 degree oven until crisply brown, about 15 minutes. Serve with garlic potatoes Sauteed in some duck fat.
* Mixed Spices: Combine 1 teaspoon each crumbled dried basil, crumbled dried thyme, freshly-grated nutmeg, ground cloves, ground white pepper, 1/2 teaspoon cayenne and 1 bay leaf, crumbled. Yield: about 2 tablespoons