Bake cake in a 9x13'' according to recipe directions. Allow cake to cool for a few minutes, then poke holes in it with a fork or wooden skewer.
Pour caramel sauce all over the cake. Then pour the sweetened condensed milk (I only usually use about 1/2 of the can of sweetened condensed milk because I think it's sweet enough with just half, the traditional recipe uses an entire can. It's up to you!) Allow the cake to cool completely.
While the cake cools, add the whipping cream to a mixing bowl and beat until soft peaks. Add powdered sugar and then beat the mixture until stiff peaks.
Smooth the fresh whipped cream over the cooled cake. Sprinkle with heath candy pieces. Refrigerate for at least 1 hour, or up to one day, before serving.
*Heath also makes a bag of chopped heath bits. It can be found near the chocolate chips at the grocery store. I use about half of the bag for this recipe.To make ahead: Make the chocolate cake up to 1 week ahead of time. Allow it to cool completely, cover it well, and store it in the freezer. Allow it to thaw overnight in the refrigerator (or leave it at room temperature for a couple hours) and then continue with step 2, poking wholes in the cake. Make the homemade caramel sauce several days in advance, to save time. It can be poured on the cake warm or cold.To freeze entire cake: Allow the cake to cool completely. Cover well and freeze for 2 months. Thaw overnight in the refrigerator.