Preheat the Oven: Preheat your oven to 350°F (177°C). Grease a 9×13-inch baking pan or line it with parchment paper for easy removal of the bars.
Make the Cookie Dough: In a large bowl, mix together the yellow cake mix, melted butter, and eggs until fully combined. Stir in the chocolate chips (and any other mix-ins you choose).
Spread the Dough: Spread the cookie dough evenly in the prepared 9×13-inch baking pan. Smooth out the top with a spatula to ensure an even layer.
Bake the Bars: Bake for 25-30 minutes or until the edges are golden brown and a toothpick inserted comes out clean.
Cool and Serve: Allow the cookie bars to cool in the pan for 5-10 minutes before cutting them into squares. Let them cool completely before serving, or enjoy them warm with a scoop of ice cream!