We opted for a standard-size (15.25 ounce) chocolate fudge cake mix. I would recommend sticking to cake mixes that call for oil as opposed to butter because the end result is much fudgier.
We like the richness that the dark chocolate chips bring to these brownies, but if you prefer, you can substitute them with semi-sweet chocolate chips or peanut butter chips.
Store the cooled brownies in an air-tight container kept at room temperature for up to 5 days. Keep them sealed with a lid to prevent them from becoming hard and crumbly.