Preheat oven to 350°F. Line a 9x13” pan with foil and spray with cooking spray.
Mix butter, egg, and cake mix in the bowl of a stand mixer fitted with the paddle attachment. You can also use a hand mixer but it will take longer. Mix until a thick cookie dough is formed. Press into the bottom of the prepared pan.
Beat cream cheese until smooth. Mix in sugar until smooth. Mix in egg, sour cream, and vanilla and beat until no lumps remain. (Your ingredients MUST be room temperature. A stand mixer does the job best, but a hand mixer will suffice if needed.) Stir in chocolate chips and pour over red velvet mixture.
Bake for about 30 minutes, until cheesecake starts to brown around the edges and is no longer wet looking (it will still jiggle slightly in the center). Cool completely to room temperature, then chill (4 hours or overnight is best) before slicing into bars.