Preheat your oven to 350°F (177°C). Prepare three 9-inch cake pans by greasing them and lining the bottoms with parchment paper.
Next, in a large bowl, whisk together the flour, cocoa powder, sugar, baking soda, baking powder, and salt. Set the bowl aside.
In a separate bowl, use a handheld or stand mixer with a whisk attachment to combine the oil, sour cream, eggs, and vanilla. Mix at medium-high speed until smooth. Then, add the room temperature buttermilk and continue mixing until fully combined.
Pour the wet mixture into the dry ingredients. Next, mix the very hot water with the espresso powder until fully incorporated. Then, add the coffee mixture to the cake batter and mix with the other ingredients until fully combined. Note that the batter will be on the thinner side, and that’s totally fine.
Evenly distribute the batter between the three prepared pans. Bake for 20-25 minutes, or until a toothpick inserted into the center of the cakes comes out clean. Oven times may vary, so check for doneness. Keep an eye on the cakes towards the end of baking.
Once done, take the cakes out of the oven and place them on a wire rack to cool. Leave them in the pans until they’re completely cooled.
While your cake is baking, make the chocolate frosting. In a large mixing bowl, beat the room temperature butter on medium speed for about 1-2 minutes until creamed. Next, add the cocoa powder, powdered sugar, salt, vanilla extract, heavy cream and espresso powder. Mix on low speed for about 30 seconds. Then, increase to high speed and beat the frosting for about 1 minute, scraping down the sides to ensure all the ingredients are incorporated. Add additional powder sugar if the frosting is too thin and more heavy cream if it's too thick (add by the tablespoon).
Assemble Cake. Place the first layer of cake on a serving plate or cake stand, and evenly spread the top of the cake layer with frosting. Next, add the second layer and repeat. Lastly, add the third layer of cake and use the rest of the frosting to frost the top and sides of the cake. Refrigerate the cake for at least 30 minutes before cutting and serving. Feel free to be creative with putting the frosting on the cake.