Good-Cooking - Orange Walnut Rum Cake with Grand Marnier Icing

Ingredients

• 1 cup butter or margarine
• 2 1/2 cups sifted all-purpose flour
• 1 cup granulated sugar
• Grated rind of 2 oranges
• Grated rind of 1 lemon
• 2 teaspoons baking powder
• 1 teaspoon baking soda
• 1/2 teaspoon salt
• 2 eggs
• 1 cup finely chopped walnuts
• 1 cup buttermilk or plain yogurt