Preheat your oven to 350°F (175°C). Lightly grease a 9x13-inch baking pan with baking spray and set it aside.

In the bowl of a stand mixer (or using a hand mixer), combine the two boxes of cake mix, eggs, milk, and canola oil. Mix on medium speed until the batter is smooth and well-blended.

Pour the batter into the prepared baking pan. Smooth the surface and bake for approximately 35 minutes, or until a toothpick inserted into the center comes out clean. Once baked, remove the cake from the oven and allow it to cool on a wire rack.

Once the cake has cooled slightly, use the handle of a wooden spoon (or a similar tool) to poke holes evenly across the surface of the cake. The holes should reach about halfway through the cake.

In a mixing bowl, whisk together the chocolate pudding mix and milk until thickened. Spoon or pipe the pudding into the holes, ensuring each cavity is adequately filled. Refrigerate the cake for 30 minutes to allow the pudding to set.

In a small saucepan, heat the heavy cream until it begins to steam but does not boil. Place the chocolate chips in a heatproof bowl and pour the hot cream over them. Allow the mixture to sit for one minute, then whisk until smooth and glossy.

Spread the ganache evenly over the chilled cake. Sprinkle the chopped Thin Mint cookies over the top while the ganache is still slightly warm to help them adhere.

Once the ganache is set, slice and serve. Store any leftovers covered in the refrigerator.