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 covered in cling wrap)

Add the sugar to a wide bottomed non-stick pan. Place on the stove on the lowest heat setting and cook until the sugar has melted. This can take ~10-15 minutes. Once the sugar starts to melt, use a clean spoon to lightly stir to encourage all of it to melt evenly. If any hard sugar lumps appear, do not worry and keep cooking as they will melt

Once the sugar has melted, continue to cook for a couple minutes on the lowest heat until it form a deep golden color, then turn off the heat

Add the room temperature butter and vigorously stir until combined. It’s ok if the mixture looks slightly separated. Then add the warmed up cream and stir vigorously until a smooth caramel sauce forms

Stir in the salt and vanilla

Pour the sauce into a bowl or jar and let cool down at room temperature for 1 hour. It will thicken up as it cools

Melt the dark chocolate in a double boiler or the microwave (in 15-20s increments). Set aside

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

Add ½ cup of the cooled down salted caramel sauce and whisk on low speed until combined. Scrape the bowl again

Add the melted chocolate (it should still be quite warm) and whisk again on low speed until combined

Lastly, add in the heavy cream and mix until combined, scraping the bowl as needed. The frosting should be smooth but slightly runny in consistency; do not overmix. If you see any hardened lumps of chocolate, remove a small amount of frosting, microwave it for 20 seconds, and mix back into the remaining frosting

Let the frosting cool down until it becomes spreadable, about 15-20 minutes in the fridge

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

Place the first cake layer onto a turntable. Spread on a layer of the frosting, then use a piping bag to pipe some frosting around the edge to create a “dam”. Pour 3-4 tbsp of the salted caramel sauce inside the dam and spread it out; the piped frosting will prevent it from flowing over the edges. Repeat with the next layer, then top off with the third cake layer

Cover the cake with a thin layer of frosting (crumb coat) and refrigerate for 20 minutes. Then slather on the remaining frosting all over. Drizzle over any remaining caramel sauce however you want to

Serve & enjoy!