Heat the oven to 350°F and grease a 9 x 13-inch baking dish. Prepare the chocolate cake mix according to the package directions, using the eggs, water, and vegetable oil listed above.

Pour the batter into the prepared baking dish and bake for 25–30 minutes, or until a toothpick inserted in the center comes out with only a few moist crumbs.

Let the cake cool for about 10 minutes. Use the handle of a wooden spoon or a large round skewer to poke holes approximately 1 inch apart across the cake, stopping before reaching the bottom.

Pour the sweetened condensed milk evenly over the holes. Warm the hot fudge sauce briefly if needed, then spread it gently across the cake.

Cool the cake completely before spreading the thawed whipped topping over the surface. Sprinkle the miniature chocolate chips evenly over the topping.

Refrigerate until well chilled, ideally for 1–2 hours, then slice and serve. Keep leftovers covered and refrigerated.