1. First, preheat your oven according to the cake mix instructions and prepare a baking pan by greasing or lining it with parchment paper. In a mixing bowl, combine the cake mix, softened butter, egg, vanilla extract, and coffee/water (if needed) until you have a smooth batter. Fold in the semi-sweet and white chocolate chips to create a decadent chocolate chip-studded base.

2. Spread the batter evenly into the prepared pan and bake according to the box directions or until a toothpick inserted comes out clean. Allow the cake bars to cool slightly before moving on to the next step.

3. In a separate bowl, combine the sweetened condensed milk, cream cheese, and vanilla extract. Beat the mixture until it’s smooth and creamy, creating a luscious filling for your chocolate cake bars.

4. Spread the cream cheese mixture evenly over the slightly cooled cake base. If desired, you can bake the assembled bars for an additional 10-15 minutes to slightly set the cream cheese layer, but this step is optional.

5. Finally, let the chocolate cake bars cool completely before slicing into perfect squares of chocolate and cream cheese heaven.