Preheat oven to 350 degrees F (175 degrees C). Spray a 10x15 inch pan with non-stick cooking spray.
In a large bowl, mix together cake mix and pudding mix. Pour in water and egg whites. Beat on low speed for 1 minute. Increase speed to high and beat for 4 minutes. Pour batter into prepared 10x15 inch pan.
Bake in the preheated oven for 25 to 30 minutes, or until a toothpick inserted into the center of the cake comes out clean. Allow to cool completely.
In a large bowl, combine milk, lemon extract and vanilla pudding mix. Beat on low for 2 minutes. Fold in whipped topping. Spread over cooled cake. Store cake in refrigerator.