Empty a 12-ounce bag of fresh or frozen cranberries into a saucepan and transfer 1/2 cup to a small bowl. Add 1 cup sugar, 1 strip orange or lemon zest and 2 tablespoons water to the pan and cook over low heat, stirring occasionally, until the sugar dissolves and the cranberries are soft, about 10 minutes. Increase the heat to medium and cook until the cranberries burst, about 12 minutes. Reduce the heat to low and stir in the reserved cranberries. Add sugar, salt and pepper to taste. Let cool.
Heat 1/2 cup cranberry juice over low heat, then stir in a 1/4-ounce packet gelatin. Puree cooled cranberry sauce with another 1/2 cup cranberry juice, then add the gelatin mixture. Pour into a mold or empty soup cans and refrigerate overnight. Serve with whipped cream.