In a large bowl combine the cake mix, 1 egg and 8 tablespoons (112 g) melted butter until well mixed.
Pat the mixture into the bottom of a greased 9x13" baking dish.
In another large bowl, using an electric mixer beat together the cream cheese, 2 eggs, vanilla, 8 tablespoons (112 g) melted butter and the juice of one lemon until smooth.
Next, gently add in all the powdered sugar and mix well.
Pour that mixture all over the cake layer and spread out evenly.
Bake for 40 to 50 minutes.
The key to this cake is to not overbake it! You want the middle to be gooey.