Preheat the Oven: Preheat your oven to 350°F (177°C) and grease a 9×13-inch baking pan with cooking spray or line it with parchment paper for easy cleanup.
Make the Dough: In a large bowl, combine the chocolate cake mix, melted butter, and eggs. Stir until fully combined. Add in the chocolate chips (or any other mix-ins) and fold them into the dough.
Spread the Dough: Spread the dough evenly into the prepared 9×13-inch baking pan. Use a spatula to smooth out the top so it’s even across the surface.
Bake the Bars: Place the pan in the preheated oven and bake for 25-30 minutes. Check the bars at the 25-minute mark by inserting a toothpick into the center. If it comes out clean, they’re ready. Be careful not to overbake them; you want them to stay soft and chewy.
Cool & Slice: Allow the bars to cool in the pan for about 10 minutes before transferring them to a wire rack to cool completely. Once they’re fully cooled, cut them into squares or rectangles and serve!
