Preheat your oven to 350 degrees Fahrenheit. Prepare Devil's Food Cake batter according to package directions.
Line cupcake tray with paper liners. Fill 15-18 cupcake liners with 1/4 cup cupcake batter.
Bake for about 20 minutes, or until a toothpick inserted in the center comes out clean. Remove the cupcakes from the oven and allow them to cool for about 5 minutes before transferring them to a wire cooling rack.
When the cupcakes are cool, use the handle of a wooden spoon to poke 3-4 holes in each cupcake.
In a bowl combine sweetened condensed milk with 1 cup caramel sauce. Pour the sauce into a piping bag or a ziplock bag. Snip the tip off and fill each of the holes with this mixture.
Now begin the frosting. In a small saucepan, combine 5 tablespoons flour with 1 cup milk. I used 1%. Stir and whisk the mixture constantly until it becomes really thick. Place this mixture in the refrigerator or freezer for about 10 minutes so that it cools completely.
When the flour/milk mixture has cooled completely, cream together butter and sugar with your mixer. When the sugar is well incorporated into the butter, add in vanilla and mix for 30 seconds longer. Add in the thickened milk/flour mixture and mix on low for about 30 seconds. Then turn to high and mix for about 3 minutes, or until the frosting is light and fluffy, much like whipped cream. If the consistency isn't like whipped cream, keep mixing!
Place the frosting in a ziplock bag or a piping bag (I use Wilton brand) and place a good amount of frosting on each cupcake. Top with Heath bar pieces for garnish.