Preheat oven to 350 degrees F. Lightly grease a 9x13-inch pan.
Combine cake mix, egg, and 1/2 cup melted butter in mixing bowl. Mix well. Press cake layer into bottom of prepared pan.
In a large mixing bowl, beat cream cheese until smooth. Add eggs, vanilla, lemon, and 1/2 cup melted butter until well combined. Mix in powdered sugar. Spread filling over cake layer.
Bake in preheated oven for 40-45 minutes or until lightly golden. Do not over bake.