Beat cream cheese in bowl with electric mixer until smooth. Gradually add in 1 cup milk until blended. Add remaining milk and pudding mix. Beat on low speed for 2 minutes. Gently stir in whipped topping.
Spread half the pudding mixture over graham squares. Top with remaining graham squares and then remaining pudding mixture. Refrigerate 4 hours or overnight.
Cut into squares to serve. Garnish with additional whipped topping, if desired.