Preheat oven to 350°F. Prepare three 9-inch round cake pans with non-stick spray and parchment paper.
In a stand mixer with whisk attachment, beat granulated sugar and eggs on high speed for 2-3 minutes until light and fluffy.
Combine hot water, cocoa powder, instant coffee, and salt in a bowl. Slowly add to sugar mixture on low mixer speed.
With mixer on low, gradually add sifted flour, baking soda, and baking powder. Mix until incorporated.
Add vegetable oil, buttermilk, and vanilla extract. Scrape bowl sides as needed. Do not overmix.
Pour batter evenly into prepared pans. Bake for 22 to 25 minutes or until a toothpick inserted comes out clean.
Cool cakes in pans for 10 minutes, then invert onto wire racks. Let cool completely or refrigerate until assembly.
Chill a clean mixer bowl with whisk attachment in the fridge for 15 minutes for whipped cream.
Whip cold heavy cream on high speed until soft peaks form.
Slowly add confectioners' sugar, Bailey's Irish Cream, Kahlua, and cornstarch while mixer is on low speed.
Whip on high until stiff peaks form. Refrigerate until ready to assemble the cake.
For ganache: Microwave dark chocolate chips and room temperature heavy cream in 15-second intervals, stirring in between, until smooth. Chill for 15 minutes.
Notes
This cake is best served chilled to keep the whipped cream firm and the ganache set. Store leftovers in the refrigerator.