To make real whipped cream filling, combine 1 box instant vanilla pudding mix, 1½ cups water and 1 (9-ounce) can sweetened condensed milk in a large bowl. Whisk until well combined. Cover and refrigerate until firm, at least 4 hours. In bowl of mixer, place 3 cups heavy whipping cream and whip until stiff peaks form. Fold in pudding mixture, half at a time, and gently combine until there are no streaks. Assemble cake as per instructions above.