Bake the Betty Crocker yellow cake in a 9x13 baking dish according to the package directions, then let it cool for 10 minutes.

Using the round handle of a wooden spoon, poke holes evenly across the entire surface of the warm cake.

In a bowl, whisk the cold milk and Jell-O vanilla pudding for 2 minutes until it begins to thicken, then immediately pour it over the cake, pressing it down into the holes.

Place the cake in the refrigerator for 2 hours to let the pudding set firmly.

Remove the foil seal from the chocolate frosting, microwave the tub for 15 seconds until easily pourable, and spread it in an even layer over the pudding. Chill for another 30 minutes before serving.