To begin, heat up the oven to 350°F (180°C). Apply a coat of nonstick cooking spray to three cake pans that are 8 inches round. Place a piece of parchment paper at the bottom of each pan, and leave them aside for now.

Combine the flour, cocoa powder, baking soda, baking powder, and salt in a big mixing bowl. Blend in the granulated sugar and brown sugar until thoroughly mixed.

Include the oil, buttermilk, eggs, and vanilla extract into the mixture and stir until only blended, the consistency of the batter should resemble that of thick brownie batter.

Incorporate the instant espresso powder into the cup of water that is boiling and continue stirring until completely dissolved. Transfer the mixture to the mixing bowl and blend until all the ingredients are just combined and the texture is even. The batter will appear very liquid.

Evenly distribute the batter among the three cake pans that have been prepared.

Cook the cakes in the oven for 25 to 30 minutes, or until a toothpick inserted into the middle of the cakes comes out free of any batter and the tops bounce back when gently pressed.

Take out of the oven and move to a wire rack to cool in the baking pans for 20 to 30 minutes. Use a knife to go around the edges of each cake layer in the pan and gently take the cakes out of the pans (if necessary, remove the parchment paper) and place them on the metal stand to cool down entirely.

Using a stand mixer with the paddle attachment or a handheld mixer in a large mixing bowl, beat the butter at medium speed for approximately 1 minute until it becomes smooth.

Add 240 grams (2 cups) of powdered sugar gradually, ensuring thorough mixing after each addition.

Combine the heavy whipping cream, vanilla extract, and salt together and mix at a moderate speed until the mixture becomes thoroughly blended and smooth.

Combine the Oreo crumbs and mix on a medium-low speed until thoroughly mixed, occasionally pausing to scrape the sides of the bowl.

You should use a knife or cake leveler to make the tops of each cake layer even.

To make the cake adhere to the surface, place a tablespoon of buttercream in the middle of a cardboard cake round or a cake stand.

Take the initial layer of cake and place it on your workspace. Use an angled spatula or the back of a spoon to spread approximately three-fourths to one cup of frosting evenly over the first layer.

Take the second cake layer and position it upside down over the frosted layer. Apply an additional three-fourth cup to one cup of frosting on the top and spread it evenly across the surface.

Place the third layer of the cake in an inverted position onto the frosted layer. Use the remaining frosting to cover the top and sides of the cake. If planning to add decorative piping on the top, set aside 1 to 1 ½ cups of frosting for later use.

Put the cake inside the fridge and allow it to become cold as you get ready the ganache.

To prepare the ganache (if desired): Place the chopped chocolate into a spacious bowl that is resistant to heat and leave it to the side.

Take the heavy whipping cream and place it in a bowl that is safe to use in the microwave, or alternatively, a glass measuring cup. Heat the cream in the microwave for a duration of 45 seconds to 1 minute. Be cautious and closely monitor the cream to prevent it from overflowing in the microwave.

Gently pour the warmed heavy whipping cream onto the chocolate and allow it to rest for a period of 2 to 3 minutes. Begin stirring gradually at the center of the bowl, and keep stirring in a single direction until the mixture becomes smooth and thoroughly blended.

Leave the mixture undisturbed for a period of 20 to 30 minutes, or until it has cooled down and become slightly thicker.

Take the cake out of the fridge. Transfer the ganache into a piping bag or squeeze bottle (or alternatively, use a spoon) and drizzle it along the outer rim of the cake. Then, pour the remaining ganache on top and evenly spread it across the cake.

After allowing the ganache to slightly harden, apply the remaining frosting on the cake using a piping bag. If preferred, garnish with more Oreos on top.