Preheat your oven to 350°F (175°C) and generously coat a 9×13-inch baking pan with nonstick cooking spray. In a large bowl, whisk together the chocolate fudge cake mix, dry chocolate pudding mix, whole milk, vegetable oil, and eggs until smooth and fully combined. Pour into the pan and bake for 30–35 minutes until a toothpick inserted into the center comes out clean.

Remove the cake from the oven. While it is still quite warm, take the rounded handle end of a wooden spoon or a thick chopstick and poke holes across the entire surface of the cake, spaced about 1 inch apart. Push down about 2/3 of the way into the cake—make sure not to poke all the way through to the bottom, or the liquid will pool underneath. Let it cool on a wire rack for 20–30 minutes.

Slowly pour the entire can of sweetened condensed milk evenly across the top of the warm cake, guiding it so it fills up the poked channels. Follow immediately by drizzling ½ cup of the caramel sauce directly into the holes. The warm, porous cake crumb will drink up these liquids as it sits.

Once the cake has completely cooled to room temperature, gently spread the thawed whipped topping over the surface in a smooth, uniform layer. Drizzle the remaining ¼ cup of caramel sauce in a clean zigzag pattern across the top. Finish by scattering the crisp toffee bits and chopped chocolate bars evenly over the surface.

Place the cake, uncovered, into the refrigerator for at least 1 hour (ideally 2 to 3 hours) to allow the crumb to fully set and solidify into its signature fudgy texture. Slice into square portions and serve perfectly chilled straight from the fridge.