- Bake at 350°F in a 9×13 inch pan for about 20 minutes, watching for the edges to turn lightly golden while the center sets but retains a soft appearance. If using a smaller pan, extend the bake time to 25–28 minutes to account for the thicker layer. The bars may appear slightly soft when first removed from the oven, but they will continue to firm up as they cool. Allow the bars to rest in the pan until they are cool enough to cut cleanly.
Serving and Storage
Once cooled, slice the cookie bars into squares or rectangles. Serve them at room temperature for the best texture, with the chocolate chips lightly set but still pleasantly tender. Any leftovers keep well in an airtight container for several days, staying soft due to the cake mix base. For longer storage, the bars can be frozen and thawed as needed.
