Bake the Cake: Preheat oven to 350°F (175°C). Prepare the yellow cake mix according to package directions. Pour batter into a greased 9×13-inch baking dish and bake as directed. Let cool for 10 minutes.

Poke the Cake: Using the handle of a wooden spoon or a similar tool, poke holes all over the warm cake, spacing them about an inch apart.

Make the Pudding: In a medium bowl, whisk together the vanilla pudding mix and cold milk until smooth and slightly thickened (about 2 minutes).

Fill the Cake: Pour the pudding over the cake, using a spatula to spread it evenly and press it gently into the holes. Refrigerate the cake for at least 1 hour to set.

Prepare the Ganache: In a small saucepan over low heat, heat the heavy cream until just simmering (do not boil). Remove from heat and stir in chocolate chips, butter, and vanilla extract. Stir until smooth and glossy.

Top the Cake: Pour the chocolate ganache over the chilled cake, spreading it into an even layer.

Chill and Serve: Refrigerate the cake for another 1–2 hours, or until the ganache is set. Slice and serve cold for best results.