Remove the cookwell from your Nesco and preheat the base at 350.
Rinse the inside of the duckling and pat dry with paper towels. Skewer neck skin to back tie legs to tail. Twist wing tips under the back. Place duckling, breast side up, on a rack in the cooking well of the Nesco. Using a fork, prick the skin generously. Do not prick the flesh, skin only. Sprinkle with salt and pepper.
Roast at 350 degrees F for 20 minutes per pound or until an instant-read thermometer reads 165 F. Remove the duck from the well, cover it and let it rest about 15 minutes before carving it.
Meanwhile, for sauce, in a small saucepan combine all the sauce ingredients except the butter. Bring to a boil. Cook, uncovered, over medium-high heat about 8 minutes or until sauce is reduced to 1/4 cup. Simmer, uncovered, about 5 minutes, stirring occasionally. Remove saucepan from heat; stir in butter until melted. Put it in a nice serving dish, and serve it with the carved duck.