Add lemon juice and sugar to pitcher.
if you are using bottled lemon juice, increase amout to 1 1/2 cups.
Stir until sugar is dissolved.
Add water and stir until well mixed.
Refrigerate at least 1 hour to chill.
Add 1 cup chilled lemonade and 2 cups (about 4 scoops) ice cream to blender.
Pour into cup and garnish with lemon slice.