1 package yellow or butter cake mix
1/4 C packed dark brown sugar
2 large eggs
1/2 C (1stick) melted butter
1 tsp vanilla
1 C chocolate chips (I used milk)
1 C Heath Toffee Bits (you could used chopped nuts instead)
Preheat oven to 350. Spray or foil line and spray a 9"x13" pan (I use foil and spray - makes the bars super easy to remove from the pan and cut).
Blend the cake mix, brown sugar, eggs melted butter and vanilla in a large bowl on low speed until well mixed. Stir in chocolate chips and toffee bits. Spread dough in prepared pan with a spatula - it will be stiff and you'll think it won't spread enough to cover the whole pan. It will.
I started with a bag each of chocolate chips and toffee bits and used the extra (along with the crushed pretzels) to sprinkle the top with before baking. Bake about 25 minutes - bars will crisp up as they set so don't over bake (should be golden brown but still soft). Let cool and cut into bars.