Preheat your oven to 350°F (175°C) and grease a 9x13-inch baking pan.
In a large bowl, stir together the cake mix and brown sugar.
Add the melted butter and eggs. Mix until everything comes together. It’ll be thick. That’s a good thing.
Fold in the toffee bits and pecans if you’re feeling a little nutty.
Press the dough evenly into your prepared pan. Use your hands—get in there.
Bake for 25–30 minutes or until the top is golden and a toothpick comes out with a few moist crumbs.
Cool completely in the pan before slicing. (Yes, the waiting is the hardest part.)