Peel and quarter potatoes and in a saucepan combine with enough cold water to cover by 2 inches. Simmer potatoes 15 to 20 minutes, or until soft, and drain in a colander. Return potatoes to pan and steam, covered, over moderate heat, shaking pan, 30 seconds to evaporate any excess liquid. Force hot potatoes through a ricer or medium disk of a food mill into a bowl and beat in sour cream and salt and pepper to taste.
Remove skin from duck legs and cut into 1/4-inch strips. In a small heavy skillet cook skin in 1 tablespoon butter over moderately low heat, stirring occasionally, until crisp and transfer cracklings with a slotted spoon to paper towels to drain.
Remove meat from duck legs and chop fine. Add garlic to fat remaining in skillet and cook over moderately low heat, stirring occasionally, until softened. Add meat to skillet and cook over moderate heat, stirring occasionally, until heated through. Stir in salt and pepper to taste. Stir meat mixture into potato mixture and cool. Filling may be made 1 day ahead and chilled, covered.
Put 1 wrapper on a lightly floured surface and mound 1 tablespoon filling in center. Top filling with 1 parsley leaf. Lightly brush edges of wrapper with water and put a second wrapper over first, pressing down around filling to force out air and sealing edges well. Trim excess dough with a round cutter or sharp knife. Make more ravioli with remaining wrappers, filling, and parsley in the same manner, transferring as formed to a dry kitchen towel and turning occasionally to dry slightly.
In a kettle of gently boiling salted water, cook ravioli in 2 batches for 2 minutes, or until they rise to the surface and are tender. (Do not let water boil vigorously once ravioli have been added.) Transfer ravioli as cooked with a slotted spoon to a dry kitchen towel to drain and keep warm.
While ravioli are cooking, in the small heavy skillet cook remaining 2 tablespoons of butter over moderate heat, swirling skillet occasionally, until nut brown in color. Remove skillet from heat and stir in truffle oil and paste.
Arrange 4 or 5 ravioli on each of 6 heated plates and spoon truffle sauce on top. Garnish each serving with cracklings and parsley leaves.
Recipe Courtesy of Gourmet Magazine