Preheat your oven to 350°F.
Spray a 9×13-inch baking dish with non-stick spray. Set aside. In a large mixing bowl combine the cake mix, 1 1/3 cups milk, oil, eggs and egg yolks. Whisk together until just combined.
15.25 ounce box lemon cake mix, 1 1/3 cups whole milk, 1/3 cup vegetable oil, 2 eggs, 3 egg yolks
Transfer the batter into the prepared baking dish, then place it into the preheated oven on the center rack. Bake for 40 minutes, or until a toothpick inserted into the center of the cake comes out clean or with a few moist crumbs.
Once baked, remove from the oven and let cool.
Once the cake has cooled down some, poke holes into it using a chopstick or wooden spoon handle.
In a large mixing bowl whisk together 2 cups of the milk and pudding until just combined. Pour evenly over the top of the cake and let it soak in.
2 cups whole milk, 3.4 ounce box Jello lemon pudding mix
Add the Cool Whip over top, then cover and place the entire cake into the refrigerator to chill for at least 4 hours or overnight.
8 ounce Cool Whip Topping
Once the cake is chilled, slice and serve.