Bake cake in a 13x9 cake pan according to package directions
Remove from oven and while warm use a wooden spoon handle or a straw to poke holes throughout.
In a medium bowl, whisk together milk and pudding mixture and continue to whisk until smooth.
Pour pudding on top of warm cake, making sure to pour straight into the holes in the cake.Take a spoon and spread it evenly across the top of the cake (very gently press down pudding to ensure that pudding goes into the holes and spread it all the way to the sides).
Put cake in fridge and allow to cool completely before adding the frosting (about 2 hours).
Take the chocolate frosting out of the tub and put it in a microwave safe bowl. Microwave it for 1 minute at 50% power. This should make the frosting pourable.
Pour over the cake and spread it out evenly.
Return to the fridge for the frosting to set up.
Serve and enjoy!
Gluten Free
Use a gluten free cake mix
Dairy Free
You can actually make the custard filling dairy free buy using your choice of dairy free milk, but halving the amount. So only 1 1/2 cups. You can use an additional box of pudding mix if desired. Also use a dairy free cake mix and dairy free chocolate frosting.