Preheat the oven to 350°F and prepare a 9x13 pan by spraying it with cooking spray.
In a medium bowl, mix the cake mix, 4 eggs, melted butter, and one cup of milk.
Pour the batter into the prepared pan and bake for 30 minutes or until a toothpick comes out clean.
While the cake is baking, combine the remaining 1 cup of milk, evaporated milk, and sweetened condensed milk in a medium bowl. Place it in the refrigerator until needed.
In a small bowl, mix together the strawberry jam and 1 cup of the sliced strawberries. Set aside.
Let the cake cool completely before poking the cake all over with a fork. Pour the milk mixture over the cooled cake, then spread the cake with the jam mixture, then the Cool Whip.
Top the cake with the remaining sliced strawberries, then cover and refrigerate for at least 1 hour.
Slice into 12 squares and serve immediately. Any leftover cake should be stored in the refrigerator.