Preheat oven to 350 degrees. Spray a 13x9 Pyrex dish with non-stick spray.
Using an electric mixer, combine the cake mix, 1 egg and 1 stick of melted butter until well combined. Pat the mixture into the Pyrex dish.
Using an electric mixer, beat the cream cheese until smooth. Add 2 eggs, vanilla and other stick of melted butter and mix until well combined.
Add the powdered sugar and mix well.
To this mixture fold in the lemon juice and zest.
Spoon this mixture over the cake batter and use a spoon to spread to create an even layer.
Sprinkle the fresh blueberries on top.
Bake for 40-50 minutes just until the cake seems set but a little gooey in the center.
Top with cool whip (optional).