Preheat your oven to 350°F (175°C). Grease three 8-inch round cake pans and line the bottoms with parchment paper. This helps the layers release cleanly.

In a large mixing bowl, whisk together the all-purpose flour, granulated sugar, unsweetened cocoa powder, baking soda, baking powder, and salt. Make sure the cocoa powder is not lumpy.

Add the eggs, buttermilk, vegetable oil, and vanilla extract to the dry ingredients. Mix until just combined. The batter will be thick at this point.

Slowly pour in the hot coffee or hot water while stirring. The batter will become thin. That is normal and creates a moist crumb. Divide the batter evenly among the three prepared pans.

Bake for 23 to 28 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs. Avoid overbaking, as that can dry out the cake. Cool the layers in the pans for 10 minutes, then transfer them to a wire rack to cool completely.

While the cakes cool, make the cookies-and-cream frosting. Beat the softened unsalted butter until pale and fluffy. Gradually beat in the powdered sugar, vanilla extract, salt, and heavy cream. Start with 3 tablespoons of cream and add more only if needed. The frosting should be thick, smooth, and spreadable.

Fold about 1 cup of the finely crushed chocolate sandwich cookies into part of the frosting. Use this cookie-packed frosting to fill the cake layers. Keep the remaining plain vanilla frosting for the outside.

Place one cooled cake layer on a serving plate or cake board. Spread a generous layer of the cookie frosting over the top. Repeat with the second and third layers. Use the remaining vanilla frosting to cover the top and sides in a thin crumb coat. Chill for 20 to 30 minutes, then add a final smooth layer of frosting if desired.

To make the ganache, place the finely chopped semisweet chocolate in a heatproof bowl. Heat the heavy cream until steaming but not boiling. Pour it over the chocolate and let it sit for 2 to 3 minutes. Stir slowly until the mixture becomes glossy and smooth.

Let the ganache cool until it thickens enough to drip slowly from a spoon. If it is too hot, the drips will run down the sides too fast. If it becomes too thick, warm it gently in short bursts.

Spoon the ganache around the chilled cake edge, pushing it slightly over the side to create drips. Continue around the cake, then spread the remaining ganache across the top with an offset spatula.

Finish the Chocolate Oreo Drip Cake with whole and broken sandwich cookies, chocolate truffles, cookie crumbs, and sprinkles. Pile the decorations high in the center for a bakery-style look.

For the cleanest slices, chill the finished cake briefly, then let each slice soften at room temperature before serving.