Preheat the oven to 350°F (180°C). Beat the cake mix with 1 1/3 cups milk, oil, and eggs until smooth and no lumps remain.

Pour the batter into 2 greased cake pans (9–10 inches, or a quarter sheet pan) using butter, and bake for 40 minutes to 1 hour, or until a toothpick inserted in the center comes out clean.

Once done, place the cakes on a wire rack and let them cool for about 1 1/2 hours. Meanwhile, whip the whipped topping until stiff peaks form.

Mix the remaining 2 cups milk with the evaporated milk and sweetened condensed milk until fully combined.

Once the cakes are cool, remove them from the pans and trim the rounded tops. Using a piping bag, pipe a border of whipped topping around the edge of the bottom cake layer, then pour the milk mixture over it until it's nicely soaked. Fill as desired*, place the top cake layer on, and repeat the process.

When both layers are soaked, cover the cake with the whipped topping and decorate as you like. Refrigerate until ready to serve.