Preheat oven to 350°F. Grease a 9x13 baking pan and line with parchment paper, then grease the parchment paper.
Make the cake:
Whisk the flour, cocoa powder, sugar, baking soda, baking powder and salt together in a large bowl. Set aside.
Using a stand mixer fitted with a whisk attachment mix the oil, eggs, and vanilla together on medium speed until combined. Add the buttermilk and mix until combined. Pour the wet ingredients into the dry ingredients, add the hot coffee, and whisk or beat on low speed until the batter is completely combined.
Pour the batter into your prepared pan. Bake for 40 minutes or until a toothpick inserted in the center comes out clean. Baking times vary, so keep an eye on yours.
Make the buttercream:
With your stand mixer, beat the butter on medium speed until creamy. Add confectioners’ sugar, cocoa powder, 3 Tablespoons heavy cream, salt, and vanilla extract. Beat on low speed for 1 minute, then increase to high speed and beat for 1 full minute.
Do not over-whip. Add ¼ cup more confectioners’ sugar or cocoa powder if frosting is too thin or 1 more Tablespoon of cream if frosting is too thick.
Place half a cup of the frosting in a piping bag with a small round tip, set aside.
Decorate the cake:
Evenly cover the top of the cake and sides with the remaining frosting with an icing spatula.
Carefully cut the milano cookies in half. Using the buttercream in the piping bag, write the letters RIP to turn the cookies into little tombstones.
Over the top of the frosted cake, sprinkle the crushed oreos and halloween sprinkles. Place the cookie tombstones around the cake to give the cake the appearance of a graveyard.