Place sweet potatoes in medium pot and fill with enough cool water to cover potatoes. Bring to a boil. Cover and cook until very tender, about 10 minutes. Drain potatoes and place in medium mixing bowl. Add orange juice, butter, milk, and pumpkin pie spice. Mix until smooth. Add salt and pepper.
Spoon mixture into 6 4-ounce ramekins and sprinkle walnuts on top. Bake twelve minutes or until walnuts are toasted.