In a bowl, combine cake mix, egg, and butter with an electric mixer. Mix well.
Pat into the bottom of prepared pan , set aside.
Still using an electric mixer beat cream cheese until smooth; add eggs and vanilla. Add powdered sugar and beat very well.
Reduce the speed of mixer and slowly pour in melted butter, mix well. Stir in the chocolate chips.
Pour filling onto cake mixture and spread evenly. Bake 40-50 minutes. Mine were closer to 50. You want the center to be a little gooey, so don't bake it past that point!
Remove from oven and allow to cool completely. If you want to drizzle melted chocolate over the top, allow it to cool for at least 15 minutes first. Allow to cool for at least another hour and then cut into bars. Enjoy!