Preheat your oven following the directions on the cake mix box. Lightly grease a 9 × 13-inch baking pan. Prepare the cake batter with the ingredients listed on the package, then pour it into the pan. Bake until a toothpick inserted in the center comes out clean, about 28–32 minutes.

Let the cake cool for about 10 minutes. While it’s still warm, use the handle of a wooden spoon or a large skewer to poke holes all over the top, spacing them about 1 inch apart.

In a medium bowl, mix the sweetened condensed milk with the caramel or butterscotch topping until well combined. Slowly pour the mixture over the warm cake, making sure it seeps into the holes. Leave the cake to cool completely.

Place the cooled cake in the refrigerator for at least 1 hour. Chilling gives the caramel time to soak into the cake, making every bite extra moist and flavorful.

Once chilled, spread the thawed whipped topping evenly over the entire cake with a spatula or the back of a spoon, creating a smooth, even layer.

Sprinkle the crushed Heath bars or English toffee bits over the whipped topping. Keep the cake refrigerated until you’re ready to serve. Cut into 12 slices and enjoy cold.