Combine 2 tablespoons of the Shaoxing wine with the soy sauce, salt and 1/8 teaspoon five-spice powder in a medium bowl. Add the duck breasts and massage the marinade into them. Place the breasts, side by side, on a plate and refrigerate, uncovered, for 12 to 36 hours; the skin will dry out and look leathery.
Mix together the remaining 1 tablespoon Shaoxing wine, pinch five-spice powder and the hoisin sauce in a small bowl. Set aside.
Preheat the oven to 350 degrees F. Heat a large, heavy-bottomed ovenproof pan over medium-low heat.
Remove the duck from the refrigerator and score the skin in a cross-hatch pattern. Place the duck in the pan, skin-side down, and gently render fat; the skin will turn a rich golden brown as it cooks. When the duck stops emitting fat, after 8 to 10 minutes, flip the breasts skin-side is up and cook for another 1 to 2 minutes. Transfer the pan to the oven and cook for another 5 minutes, or until the breasts reach an internal temperature of 135 degrees F for medium; they should be pink and firm in the center.
Immediately remove the duck to a plate or carving board. Using a pastry brush, paint a thin layer of the hoisin mixture onto the skin. Let rest for 10 minutes before carving.
To serve, slice the breasts at an angle, about 1/4-inch thick, and fan out on a plate. Top with sliced scallions.
Shaoxing rice wine can be found at Asian specialty markets or online.