Heat oven to 177°C (163°Cfor dark or nonstick pan). Make and bake cake as directed on box for 33x23-cm pan. Cool 15 minutes.
Poke top of warm cake every 1 cm with handle end of wooden spoon. Drizzle condensed milk evenly over top of cake; let stand until milk has been absorbed into cake. Drizzle with caramel topping. Run knife around sides of pan to loosen cake. Cover and refrigerate about 2 hours or until chilled.
Spread whipped topping over top of cake. Sprinkle with toffee bits. Store covered in refrigerator.