In a large mixing bowl, add eggs, oil, buttermilk, pumpkin puree and mix until smooth.
Add flour, sugar, cocoa powder, pumpkin pie spice, baking powder, baking soda and mix until just combined. Don't over-mix!
Stir in chocolate chips until evenly distributed.
Pour batter in a greased and floured rectangle cake pan (Dimensions: 9x13). You can line with parchment paper, if you like. Use a spatula to spread batter evenly.
Bake at 350 degrees F for 30-40 minutes or until an inserted toothpick in the center comes out clean.
Remove from oven and allow the cake to cool to room temperature.
While the cake is baking and cooling, prepare the frosting.
In a large mixing bowl, add butter, cream cheese, pumpkin puree, pumpkin pie spice and mix until smooth.
Mix in powdered sugar gradually (½ cup at a time) until frosting is smooth and creamy without any lumps.
Spread this frosting on top of your cooled cake with a spatula. You cake is ready to be enjoyed. However, you can take it a step further and decorate it to look like a pumpkin patch, if you like.
Spread Oreo cookie crumbs on top of the iced cake as evenly as possible. This creates the illusion of dirt.
Place some pumpkin candies, stone candies randomly on top. Also, push some edible grass candy randomly between the pumpkins and stones.
Finally, create the illusion of a fence by pushing mini pretzel sticks along the 4 sides of the cake. Enjoy.