Trim excess fat from duck (do not remove skin). Score the skin in a diamond pattern. Season duck breasts with salt and pepper. In a 4-quart Dutch oven, cook duck breasts, skin side down, over medium heat for 5 minutes. Turn and cook about 5 minutes more or until browned. Drain off fat, reserving 2 tablespoons fat. Remove duck; set aside. (If using chicken, brown chicken on both sides in 2 tablespoons olive oil; set aside.)
Add onion, celery and garlic to the Dutch oven. Cook and stir over medium heat for 4 minutes. Add broth, tomato sauce, wine and bay leaves. Bring to boiling; reduce heat. Remove skin from duck and discard. Cut duck or chicken into 1-inch pieces. Add duck or chicken to pan. Simmer, covered, for 20 minutes. Stir in peas and carrots and sage. Cook, uncovered, for 8 to 10 minutes or until peas and carrots are tender, stirring occasionally.
Remove bay leaves; discard. Stir half of the Potato Topper into stew until blended. Spoon remaining potato topper into 6 mounds in shallow soup bowls. Spoon stew around potatoes; sprinkle with chives. Makes 6 main-dish servings.
Peel and quarter potatoes. In a medium saucepan, cook potatoes and salt, covered, in enough boiling water to cover for 20 to 25 minutes or until tender; drain. Mash with a potato masher or beat with an electric mixer on low speed. Add butter. Season to taste with salt and ground black pepper. Gradually beat in milk to make potato mixture light and fluffy. Set aside. Makes about 4 cups.