Mashed Potatoes with horseradish

6 medium potatoes , Peeled and Cubed 1/4 cup butter or 1/4 cup margarine , melted 3/4 teaspoon salt 1/8 teaspoon pepper 1/2 cup sour cream 2 tablespoons[...]

4 russet potatoes , about 2 lb total, peeled and cut into rounds 1/4 inch thick 3 parsnips , about 3/4 lb total, peeled and cut into rounds 1/4 inch thick 4[...]

5 medium potatoes water , Boiling 1/2 teaspoon salt 2 tablespoons butter pepper , Freshly Ground 1/2 cup sour cream 1 tablespoon horseradish 2 teaspoons[...]