4-6 Heath candy bars, crushed (I have also seen Heath bits over on the baking aisle by the chocolate chips- those would work perfectly too)
Prepare and bake cake in a 9x13" baking pan as directed on back of cake mix. Let cake cool. Using a fork, poke holes all over the top of the cake. Mix together the sweetened condensed milk and caramel topping and pour all over the cake, letting it sink down into the holes. Spread whipped topping over the caramel layer and sprinkle with crushed Heath bars.
I keep this cake in the fridge- it's delicious cold!