Preheat the oven to 350°F (175°C). Lightly coat a 9×13-inch baking dish with nonstick spray to prevent sticking and ensure clean removal after baking.

In a large mixing bowl, combine the cake mix and softened butter. Using an electric mixer, beat until the mixture forms a crumbly texture. Add two eggs and continue mixing until a thick, cohesive batter forms. Spread the batter evenly into the prepared baking dish, pressing gently to create a uniform base layer.

In the same mixing bowl, beat the softened cream cheese until smooth and creamy. Add the powdered sugar and cocoa powder, mixing until fully incorporated. Add the remaining two eggs and vanilla extract, and continue mixing until the mixture is smooth and free of lumps.

Carefully spread the cheesecake mixture evenly over the chocolate base layer. Use a spatula to smooth the surface and ensure even coverage.

Place the baking dish in the preheated oven and bake for approximately 45 minutes. The edges should appear set, and the center should no longer appear wet. Avoid overbaking, as the dessert will continue to set as it cools.

Remove from the oven and allow the dessert to cool completely in the pan before slicing. Cooling ensures clean cuts and proper texture development. Slice into 12 portions and serve.