Preheat oven to 350ºF degrees. Line four 6-inch round baking pans with parchment paper and spray with nonstick cooking spray. Add the espresso powder to the hot water, and stir until fully dissolved; set aside to cool.

In a large mixing bowl, whisk together the flour, cocoa powder, baking soda, baking powder, salt, crushed Oreos, and both sugars until well combined. Add the oil, yogurt, and espresso liquid and continue stirring with a whisk. Stir in the egg, followed by the vanilla.

Pour batter into prepared baking pans and bake in the oven for 23-25 minutes, or until a toothpick inserted in the center comes out clean. Allow cakes to cool in the pan for 10 minutes before transferring to a wire rack to cool completely.

In the bowl of a stand mixer fitted with the paddle attachment, beat the butter and salt on high until fluffy, about 4 minutes. Add the powdered sugar, a cup at a time, until fully incorporated. Mix on high for 3 minutes. Add the vanilla and heavy cream and continue beating until fluffy, about 2 minutes.

Remove 1 cup of the frosting and set aside for the filling. Add the 1/3 cup of finely crushed Oreos to the bowl of buttercream and beat until combined. Transfer buttercream to a separate bowl, then return bowl to mixer.

In the mixer, beat the cream cheese and reserved 1 cup of buttercream on high until creamy. Add half of the whipped cream, and continue beating until combined. Remove bowl from mixer, and fold in the rest of the whipped cream along with the coarsely chopped Oreos.

Place chocolate into a medium bowl. Pour heavy cream into a small saucepan on the stove and heat over medium-high heat until it begins to boil. Immediately pour hot cream over the chocolate, cover bowl in plastic wrap, then allow to sit for 3-4 minutes. Remove plastic wrap and stir until smooth. Set aside to cool slightly.

Place one cake layer on cake pedestal or plate. Top with 1/3 of the filling. Repeat with the remaining cake layers and filling. Place filled cake into the freezer for at least an hour to firm up the filling as well as to ensure easier frosting. Remove cake from freezer, frost top and sides with buttercream. Pour ganache over the top of the cake, allowing some to drip down the sides. Top with desired cookies and candy.

If not serving right away, cake can be wrapped loosely with plastic wrap and stored in the refrigerator for up to a week.