Preheat your oven to 325°F and grease a deep 9x13 cake pan with nonstick spray. Set it aside.
In a large mixing bowl, combine the cake mixes, eggs, oil, milk, and cold water. Use a hand or stand mixer to beat the mixture until smooth and lump-free. The batter will be thin, which is exactly what you want.
30 ounces box white cake mixes, 6 large eggs, 1 cup vegetable oil, 1 cup cold water, 1 cup whole milk
Pour the batter into the prepared cake pan and bake for 50-60 minutes, or until a toothpick inserted into the center comes out clean. Let the cake cool for about 20 minutes.
Using the handle of a wooden spoon, poke holes in the cake about an inch apart. Be careful not to poke all the way through; aim for just over halfway down.
In a medium mixing bowl, dissolve the cranberry jello in boiling water. Stir until fully dissolved, then transfer it to a pourable container. Slowly pour the jello over the cake, focusing on filling the holes first, then covering the remaining surface. Cover the cake and refrigerate for at least 4 hours to let the jello set.
3 ounces box cranberry Jello, 1 cup boiling water
In a separate bowl, mash the cranberry sauce with a fork or spoon until it has a smoother, more spreadable consistency. Fold the Cool Whip into the cranberry sauce until fully combined.
8 ounces tub Cool Whip, 15 ounces can whole berry cranberry sauce
Spread the cranberry whipped topping evenly over the chilled cake. Slice, serve, and enjoy!