Preheat your oven to 350°F (175°C). Grease a 9x13-inch baking dish with cooking spray or butter.
In a large mixing bowl, combine the chocolate cake mix, chocolate pudding mix, milk, vegetable oil, eggs, and vanilla extract. Mix until well combined and smooth.
Pour the batter into the prepared baking dish, spreading it evenly.
Sprinkle the chocolate chips and mini marshmallows evenly over the top of the batter.
Sprinkle the crushed chocolate cookies over the marshmallows and chocolate chips.
Bake in the preheated oven for 30-35 minutes, or until the edges are set and a toothpick inserted in the center comes out mostly clean.
Allow the cake to cool for about 10-15 minutes before serving. Dust with powdered sugar if desired.