Preheat your oven to 350°F (175°C) and prepare a 9×13-inch baking pan with parchment paper or aluminum foil and cooking spray.

In a mixing bowl, combine the yellow cake mix, melted butter, and egg until a thick dough forms.

Press two-thirds of the dough evenly into the bottom of the prepared pan.

Sprinkle the chocolate chips and toffee bits over the dough base.

Pour the sweetened condensed milk over the chocolate and toffee layer.

Crumble the remaining dough over the milk layer, leaving some gaps visible.

Bake for 25 to 30 minutes until the top is golden brown and the center is softly set.

Cool the bars completely in the pan for about 30 minutes, then slice into squares.