Preheat the oven and prepare the pan

• Preheat the oven to 350°F.
• Spray a 9x13 baking dish with cooking spray and set it aside.

Make the vanilla pudding

• Whisk the milk and the vanilla instant pudding together in a medium bowl for 2 minutes or until it starts to thicken.
• Let it rest for 4 minutes, then cover it with plastic wrap and chill while you make the cake.

Heat the milk and butter

• Combine the remaining milk and butter in a large microwave-safe bowl or measuring cup.
• Heat in the microwave in 1-minute intervals until the butter is completely melted and the milk is steaming.

Mix the cake batter

• In a large mixing bowl, add the cake mix, eggs, and milk mixture.
• Use an electric mixer to mix the batter together until just combined.

Bake the cake

• Pour the batter into the prepared baking dish.
• Bake for 25 minutes or until the cake is slightly brown on top and a toothpick poked in the middle comes out clean.
• Rest the cake on a cooling rack at room temperature until completely cool.

Make the chocolate ganache

• Pour the heavy whipping cream into a small, microwave-safe bowl, and heat in 1-minute intervals until steaming.
• Add the chocolate chips and corn syrup and let them stand for 3 minutes.
• Stir the mixture until the chocolate chips have melted and the ganache is smooth.

Assemble the poke cake

• Use the end of a wooden spoon or a thick skewer to poke holes in the cake about 1 inch apart.
• Spoon the set vanilla pudding over the cake, and spread it out evenly, ensuring that the pudding fills the holes.
• Pour the ganache over the cake, and smooth it out.

Chill and serve

• Cover the cake with plastic wrap and chill in the fridge for at least 3 hours or until the ganache has set.
• Serve chilled.