Preheat the oven to 350 degrees F. Prepare three 9-inch round cake pans with non-stick spray and/or parchment paper.
In the bowl of a stand mixer with the whisk attachment, beat the granulated sugar and eggs on high for 2-3 minutes until light and fluffy.
In a separate bowl, combine the hot water, cocoa powder, instant coffee, and salt. With the mixer on the lowest setting, slowly add this mixture to the sugar mixture.
Gradually add in the sifted flour, baking soda, and baking powder to the mixer on low speed until just incorporated.
Add the vegetable oil, buttermilk, and vanilla extract to the mixture. Scrape down the sides and bottom of the bowl as needed. Be careful not to overmix.
Evenly pour the batter into the prepared cake pans and bake for 22 to 25 minutes, or until a toothpick inserted into the center comes out clean.
Allow the cakes to cool in the pans for 10 minutes before transferring them to a wire rack to cool completely. You can also chill them in the fridge until ready to assemble.
Chill a clean stand mixer bowl with the whisk attachment in the fridge for 15 minutes.
Remove the bowl from the fridge and place it on the mixer. Add the cold heavy cream and whip on high until soft peaks form.
Reduce the mixer speed to low and slowly add in the confectioners’ sugar, Bailey Irish Cream, Kahlua, and cornstarch.
Once everything is fully incorporated, turn the mixer back to high and whip until stiff peaks form. Transfer the whipped cream to the fridge until ready to assemble.
In a medium microwave-safe bowl, combine the dark chocolate chips and heavy cream. Microwave on high in 15-second intervals, stirring with a fork after each interval, until the chocolate is melted and the mixture is smooth (about 45 seconds total).
Transfer the ganache to the fridge to cool for 15 minutes.
Place one cake layer on a serving plate. Spread a layer of Kahlua whipped cream on top.
Repeat with the remaining cake layers and whipped cream, stacking them on top of each other.
Pour the cooled ganache over the top cake layer, allowing it to drip down the sides.
Sprinkle chopped chocolate sandwich cookies over the ganache.
Chill the cake in the fridge until ready to serve.