1Heat oven to 350°F (325°F for dark or nonstick pan). Make and bake cake as directed on box for 13x9-inch pan. Cool 15 minutes.
2Poke top of warm cake every 1/2 inch 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.
3Spread whipped topping over top of cake. Sprinkle with toffee bits. Store covered in refrigerator.