Preheat the oven to 350°F. Line a 9×13-inch baking pan with foil for easy cleanup, lightly coat it with nonstick cooking spray, and set it aside.

Place the yellow cake mix, eggs, water, and oil in a large mixing bowl. Beat with a handheld electric mixer on high speed for about 2 minutes, or until the batter is smooth and evenly combined.

Pour the cake batter into the prepared pan and spread it evenly. Bake for approximately 23 to 25 minutes, or until a toothpick inserted into the center comes out clean.

Remove the cake from the oven. While it is still warm, use the rounded handle end of a wooden spoon to make holes evenly across the entire surface, reaching almost to the bottom without piercing completely through the cake.

In a medium bowl, whisk together the butterscotch topping and sweetened condensed milk until smooth and well blended.

Slowly pour the butterscotch mixture evenly over the warm cake. Gently spread it across the surface with a spatula, encouraging the sauce to flow into the holes.

Cover the cake and refrigerate for at least 2 hours, or until completely chilled and the filling has had time to soak into the cake.

When ready to serve, spread the thawed whipped topping evenly over the chilled cake.

Sprinkle the toffee bits generously across the top. Slice the cake into portions and serve chilled.