Prepare yellow cake in a 9×13-inch baking pan according to package instructions. Let cool completely.
Once cake has cooled, poke holes all over the cake using the end of a wooden spoon.
While cake cools, whisk together the instant pudding, milk, and vanilla extract in a large bowl. Before the pudding has a chance to set up and thicken, pour it evenly over the cake. Place in refrigerator to chill for one hour.
Once cake has chilled, make the chocolate ganache:
Place chocolate chips in a heatproof bowl and heat cream until simmering on the stovetop over low heat. (You can also heat it in the microwave.)
Pour hot cream over chocolate chips and let sit for 5 minutes to soften the chocolate. Stir until smooth and let cool for 10 minutes.
Pour chocolate over cake and smooth with a spatula. Chill in refrigerator at least 4 hours and up to overnight before slicing and serving.
Enjoy!
