Follow these simple steps to create your Decadent Cookies & Cream Ice Cream Cake:

1. Prepare the Cake Base: Preheat your oven to 350°F (175°C). Grease and flour a 9-inch round cake pan.

2. Mix Cake Batter: In a large bowl, combine the cake mix, eggs, water, and vegetable oil. Mix until smooth.

3. Bake the Cake: Pour the batter into the prepared cake pan. Bake for 25-30 minutes or until a toothpick comes out clean. Let it cool completely.

4. Prepare Ice Cream Layer: While the cake cools, remove the vanilla ice cream from the freezer to soften for about 15 minutes.

5. Layer Ice Cream: Once the cake has cooled, slice it horizontally in half to create two layers. Place the bottom layer back in the cake pan.

6. Add First Layer of Ice Cream: Spread 3 cups of the softened vanilla ice cream over the bottom slice. Even it out with a spatula.

7. Sprinkle Cookie Crumbs: Generously sprinkle half of the crushed chocolate sandwich cookies over the layer of ice cream.

8. Add Second Layer of Ice Cream: Spread the remaining ice cream over the cookie crumbs, smoothing it out nicely.

9. Layer Cake: Carefully place the top layer of the cake onto the ice cream. Press down gently to secure it.

10. Optional Layer: If desired, spread cookie butter here before adding the final ice cream layer.

11. Freeze Layered Cake: Cover the cake with plastic wrap and freeze for at least 4 hours, or until firm.

12. Prepare Whipped Cream: Just before serving, whip the cream until stiff peaks form.

13. Top Cake: Remove the cake from the freezer. Spread the whipped cream on top and sides of the cake.

14. Decorate: Drizzle chocolate syrup over the whipped cream and sprinkle the remaining cookie crumbs on top.

15. Slice and Serve: Carefully slice the cake with a warm knife for clean cuts.