Bake cake according to package directions for a 9X13 inch pan, then poke holes in it with a wooden spoon handle about an inch apart.
Crush the chocolate bars, reserve 1/4 cup for the top.
In the microwave, heat up the caramel in a pyrex glass measuring cup until it can be poured easily. (about one minute) Slowly pour the warm topping mixture over the top of the warm cake, letting it sink into the holes, then pour the Eagle brand sweetened condensed milk over it. (Be sure the condensed milk is at room temperature so it will pour.)
Sprinkle the crushed chocolate bars liberally across the entire cake while still warm. You can do chunks or crumbs. (I like chunks.)
Let the cake cool completely on a rack in the fridge. Then top with whipped cream frosting--recipe below. Refrigerate and serve right from the pan. Flavors meld the best when allowed to sit overnight.
Whip the 1 1/2 cup of heavy cream and the 1/4 cup of sugar until very stiff. Frost and decorate the top of the cake with some more chocolate toffee bar chunks or pulverized candy, and then add swirls of caramel topping.
Cooks tip: I use a Devil's Food Cake mix that is 50% less fat and you would never know it! (Every little bit helps!) Enjoy!