Step 1: Preheat your oven to 350°F (175°C).
Step 2: Grease your 9x13-inch baking pan with cooking spray or butter.
Step 3: In a large mixing bowl, combine the yellow cake mix, melted butter, and egg until well combined.
Step 4: Press about two-thirds of the cake mix mixture into the bottom of the prepared baking pan.
Step 5: Sprinkle both bags of chocolate toffee bits evenly over the pressed cake mix layer.
Step 6: Pour the sweetened condensed milk over the toffee bits and spread evenly.
Step 7: Crumble the remaining cake mix mixture over the top of the condensed milk layer.
Step 8: Bake for 25-30 minutes, or until the top is golden and the edges are bubbling.
Step 9: Let cool completely before cutting into squares to serve.
