Preheat oven to 300°F (150°C). Prepare three 8-inch cake pans with parchment paper circles in the bottom and grease the sides.

In a large bowl, whisk together all dry ingredients (flour, sugar, cocoa powder, baking soda, salt).

Add eggs, milk, and vegetable oil to the dry ingredients and mix well until combined.

Add vanilla extract to the boiling water, then slowly add this mixture to the batter, mixing well until smooth.

Divide the batter evenly among the three prepared cake pans. Bake for about 30-33 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs.

Remove cakes from the oven and allow them to cool in the pans for about 10 minutes before inverting them onto wire racks to cool completely.

While cakes cool, begin making the icing. In a large bowl, beat the unsalted butter until smooth and creamy.

Gradually add 4 cups of powdered sugar, mixing until smooth.

Stir in vanilla extract, Oreo crumbs, and a pinch of salt, mixing until fully incorporated.

Add the remaining 4.5 cups of powdered sugar, mixing until smooth. Add heavy cream, 1 tablespoon at a time, until the buttercream reaches a smooth and spreadable consistency.

Measure out about 3.5 cups of the Oreo buttercream and fold in the chopped Oreos for the cake filling. Set this chopped Oreo filling aside. Keep the remaining plain Oreo buttercream aside for frosting.

Once cakes are completely cool, use a large serrated knife to level the tops, removing any domes.

Place the first cake layer on your serving plate or cake stand. Spread half of the chopped Oreo filling evenly over the top.

Add the second cake layer and spread the remaining chopped Oreo filling evenly on top.

Place the final cake layer on top. Use the plain Oreo buttercream to frost the entire outside of the cake, aiming for a smooth finish.

To make the chocolate ganache, place chocolate chips in a medium-sized heatproof bowl.

Heat the heavy whipping cream in a small saucepan until it just begins to boil. Pour the hot cream over the chocolate chips. Let it sit undisturbed for 2-3 minutes, then whisk until smooth and glossy.

Drizzle the chocolate ganache around the edge of the frosted cake, allowing it to drip down the sides. Then, pour the remaining ganache over the top of the cake and spread evenly.

Allow the ganache to set slightly. Pipe any remaining Oreo buttercream around the top edge of the cake and add an Oreo between each swirl for decoration. Sprinkle with a few extra Oreo crumbs, if desired.

Serve and enjoy! The cake is best when covered and stored for 3-4 days.