In a large pitcher, combine oranges and mint leaves. Using a muddler or the back of a spoon, gently crush oranges and mint leaves. Pour lemonade into pitcher.
If desired, rub a lemon slice around rims of eight 16-ounce tall glasses and dip rims in superfine sugar. Fill glasses with ice. Pour lemonade mixture into ice-filled glasses. Garnish with the remaining sliced lemon.