- Preheat the oven: Preheat the oven to 350°F (175°C) and lightly grease a 9×13-inch baking pan.
In a medium bowl, combine the chocolate cake mix, melted butter, and 1 egg. Mix until a thick dough forms. Press evenly into the bottom of the prepared pan to form the crust.
- Prepare the filling: In a large bowl, beat the cream cheese and peanut butter until smooth and creamy. Add the remaining 2 eggs and vanilla extract, mixing well. Gradually beat in the powdered sugar until fully incorporated and smooth. Stir in mini chocolate chips if using. Pour the filling over the crust and spread evenly.
- Bake: Bake for 35–40 minutes, or until the edges are set but the center is still slightly jiggly—do not overbake.
- Cool and chill: Let cool completely in the pan, then refrigerate for at least 2 hours before slicing into bars. Serve chilled or at room temperature.