Preheat your oven to 350°F (175°C).
Grease a 9x13 inch baking dish with nonstick spray.
In a large mixing bowl, combine the box cake mix with eggs and milk.
Stir until smooth and well-combined.
Pour the batter into your prepared baking dish and bake for 25-30 minutes or until golden brown and a toothpick comes out clean.
While your cake cools slightly, whisk together sweetened condensed milk, evaporated milk, and whole milk in a separate bowl until well combined.
Poke holes all over your cooled cake with a fork or skewer.
Slowly pour the milk mixture over the top so it seeps into every nook and cranny.
In another bowl, beat heavy cream with sugar and vanilla extract until soft peaks form.
Spread whipped cream over the top of your soaked cake evenly.
Chill in the refrigerator for at least an hour before serving.
Cut into squares and serve.