Preheat your oven to the temperature specified on the yellow cake mix box (usually 350°F/175°C). Grease a 9x13-inch baking pan with nonstick spray or a thin layer of butter, making sure to coat the corners.

In a large mixing bowl, combine the yellow cake mix, eggs, oil, and water (or water/milk mixture). Beat with an electric mixer on medium speed for about 2 minutes, scraping down the sides once, until the batter is smooth and slightly thick.

Pour the batter into the prepared 9x13-inch pan and spread it evenly. Bake according to the package directions (usually 25–30 minutes), or until the top is golden and a toothpick inserted in the center comes out clean or with a few moist crumbs.

While the cake bakes, stir together the caramel sauce and sweetened condensed milk in a medium bowl until smooth and glossy. This will be the mixture that soaks into the poke cake.

When the cake is done, let it cool for about 5–10 minutes, just until it’s no longer bubbling hot. Using the handle of a wooden spoon, a chopstick, or a thick straw, poke holes all over the cake, spacing them about 1 inch apart and going almost to the bottom of the pan.

Slowly pour the caramel–sweetened condensed milk mixture evenly over the warm cake, aiming to get some into each hole. Use a spatula to gently nudge it across the top so it seeps in. If using, sprinkle a tiny pinch of flaky salt lightly over the caramel layer to balance the sweetness.

Drizzle the chocolate syrup evenly over the top of the cake in a zig-zag pattern. You don’t need to drench it; just cover the surface lightly to add chocolate flavor.

Let the cake cool completely to room temperature on the counter. Cover the pan with plastic wrap or foil and chill in the refrigerator for at least 2–4 hours, or overnight, until the cake has absorbed the caramel mixture and is well chilled.

Once the cake is thoroughly chilled, spread the thawed whipped topping evenly over the surface. Smooth the top with a spatula to create an even frosting layer.

Crush the Butterfinger candy bars (in their wrappers or in a zip-top bag) using a rolling pin or mallet until you have a mix of crumbs and small chunks. Sprinkle the crushed Butterfingers generously over the whipped topping and press very lightly so they adhere without smashing the topping.

Cover the cake again and chill for at least 30 minutes before serving. Slice into squares and serve cold. Keep any leftovers covered in the refrigerator.