Using a stand mixer, or large bowl and hand mixer, combine the cake mix, milk, water, eggs, oil, and vanilla. Mix on low speed for 1 minute then increase to medium speed 2 minutes. The batter should be mostly smooth but may have a few small lumps.

Pour the batter into the baking dish, and bake for 23-25 minutes or until a toothpick inserted in the center comes out clean.

Allow the cake to cool for about 30 minutes before adding the topping.

While the cake cools, make the milk topping. In a medium bowl, combine the sweetened condensed milk, evaporated milk, and heavy cream. 

Once the cake has cooled for 30 minutes, use a skewer to poke small holes throughout the cake. Don’t press the skewer all the way through to the bottom. Only go about ⅔ - ¾ through the cake.

Slowly pour the milk mixture over the cake, then use a spatula to evenly distribute it into the holes.

Cover the cake with plastic wrap, and transfer it to the refrigerator to finish cooling (about 1 hour).

While the cake is in the refrigerator, make the whipped cream topping. Using a stand mixer, or large bowl and hand mixer, combine heavy cream, powdered sugar, and vanilla. Beat on medium speed until stiff peaks form.

After the cake has cooled completely, add the whipped cream to the top in an even layer.