01 - Preheat oven to 350°F. Grease 9x13 inch baking pan or line with parchment paper.
02 - Combine cake mix, melted butter, and egg in large bowl. Mix until soft dough forms.
03 - Press dough evenly into prepared baking pan to form base layer.
04 - Bake for 15 minutes until just set but not browned.
05 - Remove from oven. Sprinkle chocolate chips evenly over hot base. Let sit 2-3 minutes until melted, then gently spread with spatula.
06 - Sprinkle toffee bits and chopped pecans (if using) over melted chocolate.
07 - Return to oven for 8-10 minutes until toppings are slightly bubbly and edges are golden.
08 - Let cool completely in pan before cutting into bars.