Preheat oven to 335°F / 170°C and prepare two 9-inch cake pans.
Put all ingredients (except hot water and espresso powder) in a large bowl and mix together until totally incorporated and free from lumps. I use a stand mixer but you can also do this by hand.
2 cups All-purpose Flour, 2 cups White Sugar, 2 Large Eggs, ⅔ cup Dutch Processed Cocoa Powder, ⅔ cup Vegetable Oil, 1 cup Milk, 2 teaspoon Baking Powder, ½ teaspoon Salt, 1 teaspoon Vanilla Extract
Dissolve the espresso powder in the hot water and then pour it into the chocolate cake batter. Mix until combined.
2 tablespoon Espresso Powder, ½ cup Hot Water
Divide cake batter evenly between cake pans and bake for 25 - 35 minutes, or until a skewer comes out clean. Bake time may vary depending on your oven so always test with a skewer before taking out of the oven.
Whip for a further minute, frosting should be silky smooth and stiff enough to pipe. If not, see notes.
Notes
Toggle the Cups/Grams button to switch between the different measurements. If your Russian buttercream isn't thick and glossy, try one of these things:If it is thin and soupy, the butter was probably too warm - place buttercream in the fridge for 10 minutes then try whipping up again. If it has curdled - the butter was likely too cold - try heating the buttercream very gently over a bain-marie until it just starts to sweat, then whip up for 5 minutes and it should be saved.