01 -
First, get your oven going at 350°F (177°C). Grab a 9×13 inch baking dish and give it a light spray with nonstick cooking spray to stop anything from sticking to the sides.
02 -
Dump the cake mix, eggs, oil, and vanilla into a big bowl and stir it all together until smooth. The mixture will feel thick and gooey. Toss in the M&Ms and chocolate chips, then gently fold them through so they’re spread out evenly.
03 -
Scoop the dough into your dish, spreading it flat with a spatula. Slide it into the hot oven and bake for 20-25 minutes. You’ll know it’s ready when the edges have a nice golden color, but the center still looks set. Don’t let it overcook unless you want it less chewy!
04 -
Leave the bars alone in the pan until they cool all the way down. This makes sure they firm up nicely. Once they’re cool, cut them into squares and enjoy!