Bake the cake: Preheat your oven to the temperature indicated on the box of your chocolate cake mix. Prepare the cake batter according to the package instructions and bake in a 9×13-inch baking dish. Let the cake cool in the pan for about 10 minutes.

Make the holes: Once the cake has cooled slightly, use the handle of a wooden spoon or a straw to poke holes all over the top of the cake, about 1 inch apart.

Prepare the mint filling: In a medium bowl, whisk together the instant chocolate pudding mix and milk until thickened, about 2 minutes. In another bowl, whip the heavy cream and peppermint extract until soft peaks form. Gently fold the whipped cream into the pudding mixture until smooth. Add a few drops of green food coloring if you’d like a minty green color for your filling.

Fill the cake: Pour the mint filling over the cooled cake, gently spreading it into the holes with a spatula so that the filling seeps into the cake. Refrigerate for at least 1 hour to allow the filling to set.

Make the chocolate ganache: In a small saucepan, heat the heavy cream over medium heat until it begins to simmer. Pour the hot cream over the chocolate chips in a heatproof bowl. Let it sit for a minute, then stir until smooth and glossy.

Top the cake: Pour the chocolate ganache over the chilled cake, spreading it evenly across the top.

Chill the cake: Refrigerate the cake for at least 2 hours, or until ready to serve, to allow the ganache to set and the flavors to meld.

Garnish and serve: Before serving, garnish with fresh mint leaves and chocolate shavings or sprinkles for a decorative touch.