Gather all ingredients.
Preheat the oven to 350 degrees F (175 degrees C). Grease a 9x13-inch baking dish with cooking spray.
Beat cake mix, water, eggs, and oil in a large bowl with an electric mixer at low speed until moistened, about 30 seconds. Beat at medium speed for 2 minutes.
Pour batter into the prepared baking dish.
Bake in the preheated oven until a toothpick inserted into the center of cake comes out clean, 21 to 25 minutes.
Poke holes immediately into warm cake with the round handle of a wooden spoon. Holes should be at 1 inch intervals and extend down to the bottom of the baking dish.
Combine pudding mix with confectioners' sugar in a separate large bowl and gradually stir in milk. Beat with an electric mixer at low speed for 1 minute; do not overbeat.
Pour 1/2 of the pudding mixture immediately over warm cake and into holes.
Let remaining pudding thicken slightly at room temperature, then spoon over the top and spread to cover. Chill in the refrigerator for at least 1 hour before serving. Store leftovers in the refrigerator.
Flavor Variations:
Yellow or white cake with butterscotch, pistachio, banana, coconut, or vanilla pudding. Chocolate cake with chocolate, vanilla, or coconut pudding.
Editor's Note
Cake directions are based on Duncan Hines yellow cake mix.