Heat oven to 350°F (175°C). Grease or line a 9x13-inch pan with parchment.

In a large bowl, mix cake mix, melted butter, and egg until a thick dough forms. Add 1 tsp water if too dry.

Stir in toffee bits and chocolate chips (optional) until evenly mixed.

Press dough evenly into the prepared pan, covering all corners.

Drizzle condensed milk over the dough and spread gently for full coverage.

Bake 20–25 minutes, until edges are golden and center is set. Toothpick should come out with moist crumbs.

Cool in pan 10 minutes, then on a wire rack. Slice once fully cooled.