Preheat oven to 350F (no fan) and prepare 3 8" pans with parchment paper and butter

In a bowl, combine the flour, baking powder, baking soda, granulated sugar, light brown sugar and salt. Whisk together until no lumps remain

In a separate bowl, whisk together the eggs, vegetable oil, buttermilk and sour cream until smooth

Add the dry ingredients to the wet in 2 additions, and gently whisk and fold until they are just combined and no big lumps remain. Do not overmix

In a separate small bowl, add the cocoa powder and instant coffee. Pour over the boiling water and whisk until a smooth shiny mixture forms

Pour the cocoa mixture onto the remaining batter, and gently fold until a chocolate cake batter forms

Divide the batter evenly between the 3 prepared cake pans

Bake for ~22-24 minutes until a toothpick inserted in the center comes out with light moist crumbs attached

Let the cakes cool in the pans for 20 minutes, then carefully remove them and place on a wire rack. Let cool completely (I recommend refrigerating for 1 hour)

Add the chocolate and corn syrup to a saucepan and heat over the lowest flame while stirring constantly until the chocolate has fully melted. Set aside

In the bowl of your stand mixer, add the room temperature cream cheese and sift in the cocoa powder, powdered sugar and salt. Use the paddle attachment and whisk on medium speed until the mixture becomes creamy (1-2 minutes). Scrape the bowl

Add the heavy cream and whisk again on low speed until a fluffy, whipped consistency is reached. Scrape the bowl in the middle. This should not take too long; avoid overmixing

At this point, the melted chocolate should be warm and runny but not very hot. Slowly pour it in while whisking on low speed until the chocolate is fully combined into the frosting. Due to the temperature of the chocolate, the frosting will become a more runny consistency

Let the frosting cool down until it becomes spreadable. I recommend doing this at room temperature for ~30 minutes but you can also do it in the fridge (it won't take too long). If it becomes too firm, remove 1 cup, microwave for just a few seconds it until it is warm, and whisk back into the remaining frosting

Once the cakes and frosting have cooled down, it's time to assemble

Use a large serrated knife to carefully trim off the domes from the cakes

Layer them on top of each other with a generous layer of the frosting in between (don't be stingy!). Cover the cake with a thin layer of frosting (crumb coat) and refrigerate for 20 minutes. Then slather on the remaining frosting all over

Serve & enjoy! This cake is best eaten at room temperature

Tip: To get a shiny look on the cake, use a blow dryer at the lowest setting and gently wave it 1 foot away from the cake