Preheat the oven to 325 degrees F. Spray three 8-inch round cake pans with non-stick spray, line with parchment paper, and spray again. Set aside.

Combine the flour, sugar, cocoa, baking soda, baking powder, and salt into the bowl of an electric mixer fitted with a paddle attachment and mix on low speed until combined.

In another bowl, combine the buttermilk, water, oil, eggs, and vanilla.

With the mixer on low speed, slowly add the wet ingredients to the dry, scraping the bottom of the bowl with a rubber spatula.

Divide the batter between the three pans (about 16 ounces in each) and bake for 20 to 25 minutes, or until a toothpick inserted in the center of the cake comes out with a few moist crumbs on it.

Cool in the pans for 10 minutes, then turn them out onto a cooling rack and cool completely.

Wrap in plastic wrap and freeze until ready to use.

Place the marshmallows on a cookie sheet lined with parchment paper and sprayed with nonstick cooking spray. Place on the middle rack of the oven, and broil the marshmallows until golden brown on top, about 30-60 seconds. Keep your eye on them!

Remove the pan from the oven and gently turn the marshmallows over and broil them again until they are golden brown on the other side.

In the bowl of a stand mixer fitted with the paddle attachment, combine the butter and powdered sugar and beat on low until blended. Add the vanilla and mix on medium speed for about three minutes

With the mixer on low speed, add the marshmallow cream and (cooled) toasted marshmallows, and mix for about one minute.

Fold in the crushed Oreos

In a microwave safe bowl, pour the cream over the chocolate chips and heat for about 45-60 seconds. Stir, and if needed, heat for another 30 seconds to melt the chocolate chips completely. Let cool to room temperature before using.

Combine the heavy cream and the chocolate chips in a microwave safe bowl. Heat the mixture for a minute and stir to melt the chocolate chips to create a ganache. Set aside.

In the bowl of a stand mixer fitted with the paddle attachment, beat the butter and cream cheese for about 2 minutes on medium-high speed.

Gradually add the chocolate ganache, scraping down the sides and bottom of the bowl as you go. Stir the mixture until smooth and silky.

With the mixer on low, gradually add the powdered sugar, followed by the vanilla and salt. Turn the mixer to medium-high speed and beat the frosting for about 5 minutes.

Before frosting the cake, use a wooden spoon to mix the frosting by hand to push out air bubbles and create a smooth and silky texture.

Level each chocolate cake layer, if needed, and then place the first cake layer, top side up, on a cake board.

Spread about half of the marshmallow Oreo filling over the cake layer and then drizzle with the chocolate ganache.

Repeat with second layer.

Place the final cake layer, top side side down, on top and cover with a thin layer of the buttercream. Freeze the cake for 10 to 15 minutes to set the crumb coat.

Finish frosting the cake with the remaining buttercream.

For the drip, you’ll want to heat up an additional 1/4 cup heavy cream, add it to the ganache and stir until the mixture is thinner, as seen above.