Preheat oven to 350°F. Line a 9x13 inch pan with foil and spray with cooking spray.
Mix butter, one egg, and red velvet cake mix in a stand mixer or hand mixer until a thick cookie dough forms. Press dough into the bottom of the prepared pan.
Beat cream cheese until smooth. Add sugar and beat until combined. Mix in remaining egg, sour cream, and vanilla extract until smooth. Stir in mini chocolate chips and pour evenly over red velvet crust.
Bake for 30 to 40 minutes, until cheesecake begins to brown on edges and no longer looks wet. It will still jiggle slightly. Cool completely, then chill 4 hours or overnight before slicing into bars.
Notes
Store bars in an airtight container in the refrigerator for up to five days. You can freeze for up to one month.