Mashed White and Sweet Potatoes

Heat oven to 325 degrees F. Rub skins of potatoes lightly with vegetable oil; prick all over with tines of fork. Place potatoes on cookie sheet on lowest shelf in oven. Bake potatoes 1 to 1 1/2 hours until easily pierced by tip of sharp knife, testing sweet potatoes after 1 hour. When potatoes are cool enough to handle, cut lengthwise in half. Scoop pulp from white potatoes into large bowl; using fork or potato masher, mash briefly. Scoop flesh from sweet potatoes into same bowl; set aside. In 1-quart saucepan bring cream and chicken broth to boil; remove from heat. With electric mixer at medium speed, slowly beat cream mixture into reserved potatoes until smooth and fluffy. Beat in horseradish, salt, and pepper (see note).