Preheat your oven to 350°F (175°C). Lightly grease a 9×13-inch baking pan with nonstick spray or butter. Lining with parchment is optional for easier removal.

In a large bowl, prepare the yellow cake mix according to the package directions, using the eggs, oil, and water (or milk for a richer cake). Beat with a hand mixer or whisk for about 2 minutes, until the batter is smooth and no dry streaks remain.

Pour the batter into the prepared 9×13-inch pan and spread it evenly. Bake for 25–30 minutes, or until the top is golden and a toothpick inserted in the center comes out clean. The cake should spring back lightly when tapped in the center.

Place the pan on a wire rack and let the cake cool for 10–15 minutes; it should be warm but not hot. Using the handle of a wooden spoon, a chopstick, or the thick end of a butter knife, poke holes all over the cake about 1 inch apart, going almost to the bottom without tearing the cake.

In a medium bowl or large measuring cup, whisk together the sweetened condensed milk and caramel ice cream topping until completely smooth.

Slowly pour the caramel–condensed milk mixture evenly over the warm, poked cake, taking your time so it seeps into the holes rather than running to the edges. Use the back of a spoon or an offset spatula to gently spread and nudge the mixture into the holes.

Let the cake cool completely to room temperature, then cover it tightly with plastic wrap. Refrigerate for at least 3 hours, or preferably overnight, to allow the caramel layer to soak in and set.

In a medium bowl, beat the softened cream cheese with a mixer until smooth and creamy. Add the powdered sugar and vanilla extract and beat again until fluffy and well combined. Gently fold in the thawed whipped topping with a spatula just until no streaks remain, keeping the mixture light and airy.

Place the Butterfinger candy bars in a zip-top bag. Use a rolling pin, heavy pan, or your hands to crush them into a mixture of fine crumbs and small chunks for good texture.

Once the cake is fully chilled and set, remove the plastic wrap. Spread the cream cheese–Cool Whip frosting evenly over the top of the cake. Sprinkle the crushed Butterfinger pieces generously over the frosting, pressing very lightly so they adhere without sinking.

If desired, drizzle caramel sauce and/or chocolate sauce over the top in a zigzag pattern. Sprinkle with a pinch of flaky sea salt to balance the sweetness, if you like. Cover the cake again and refrigerate for 30–60 minutes before serving to let everything set.

Slice the chilled cake into squares and serve cold. For cleaner cuts, run a knife under hot water, wipe it dry, and then slice. Store leftovers covered in the refrigerator.