1. To make the chocolate cake layers, prepare three 8 inch cake pans with parchment paper circles in the bottom, and grease the sides. Preheat oven to 300°F (148°C).
2. Add all dry ingredients to a large bowl and combine.
3. Add eggs, milk, vegetable oil and vanilla to the dry ingredients and mix well.
4. Slowly add water. Mix well.
5. Divide batter evenly between cake pans and bake for about 30-33 minutes, or until a toothpick comes out with a few crumbs.
6. Remove cakes from oven and allow to cool for 3-4 minutes, then remove to cooling racks to cool completely.
7. To make the Oreo dirt frosting, add the butter and shortening to a large mixer bowl and beat until combined.
8. Add about half of the powdered sugar and the Oreo crumbs and beat until well combined.
9. Add the vanilla extract and 3 tablespoons of water or milk and mix until well combined.
10. Add the remaining powdered sugar and Oreo crumbs and mix until well combined and smooth.
11. Add additional milk or water until the right consistency is reached.
12. To build the cake, use a large serrated knife to remove the domes from the tops of the cake layers.
13. Place the first cake layer on a serving plate or cardboard cake circle and top it with about 3/4 cup of frosting.
14. Pipe a small dam around the outside edge of the cake, on top of the frosting, then add about 1/2 cup of Oreo Crumbs. Place 6-8 gummy worms around the crumbs and gently press them down into the crumbs.
15. Add the second layer of cake, then top with another layer of Oreo frosting.
16. Repeat step 14.
17. Top the cake with the final layer of cake, then frost the outside of the cake with the remaining Oreo frosting.
18. Use the remaining Oreo crumbs to press them into some areas around the outside of the cake to make it look “dirty”.
19. To make the green frosting, add the butter to a large mixer bowl and beat until smooth (if you can, since it’s such a small amount).
20. Add the powdered sugar and mix until well combined and smooth.
21. Add the vanilla extract and one tablespoon of water or milk and beat until smooth. Add additional water or milk, if needed to get the right consistency.
22. Use the green gel icing color to color the frosting green.
23. Use Wilton icing tip 233 (the grass tip) to pipe grass around the top edge of the cake and few places on top. Place a few more gummy worms around the top of the cake and finish it off with the remaining Oreo crumbs.