- 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.