Preheat the oven to 350 F/180 C. Line two 8-inch round cake pans with parchment paper on the bottoms and set them aside.

In a stand mixing bowl, combine the flour, sugar, brown sugar, baking soda, baking powder, salt, and espresso. Add in the butter and mix for 3 minutes on low until it resembles coarse sand.

Add in the sour cream and oil. Mix on low speed for exactly one minute. It should be a very thick paste.

In a bowl with a spout, whisk together the eggs, milk, and vanilla. In a separate bowl, whisk together the HOT coffee and cocoa powder.

With the mixer running on low, slowly stream the egg mixture into the batter and mix until just combined. Then, immediately follow with the coffee/cocoa mixture, mixing until just combined. Scrape down the bottom of the bowl to make sure there are no streaks of pale batter.

Evenly distribute the chocolate batter into both cake pans. About 725 grams in each.

Bake for 33-36 minutes, or until a toothpick inserted into the center comes out mostly clean, with a few moist crumbs clinging to it.

Let the pans cool on a wire rack for 20 minutes, then run an offset spatula around the sides of the pan. Flip each pan over to release the cake. Allow them to continue cooling completely on the rack.

While the cakes cool, make the frosting. In a stand mixing bowl, cream the butter, cocoa powder, and powdered sugar together on low speed until combined.

Increase the speed to medium-high and mix for 3 minutes, until very light and fluffy.

Then mix in the coffee, heavy cream, vanilla, and salt. Mix on low until combined, then increase the speed to medium and mix for another minute until light and fluffy again.

In a small pot, whisk together the cocoa powder, sugar, coffee, water, vanilla, and salt. Cook over medium heat until it starts to boil, then reduce the heat to low and cook for 2-3 minutes until thickened. Pour into a bowl and set aside until ready to use.

Use a serrated knife to cut the dome off both layers. If making four layers, carefully cut each layer in half. You can skip this step and just make a two-layer cake instead!

Pipe a dollop of buttercream onto a cake round or serving platter and place the first layer on top. Drizzle 1 tablespoon of the chocolate coffee syrup over the exposed crumb.

Evenly spread about ¼ cup of the buttercream over the cake, then place the next layer. Continue with these steps, flipping the last layer upside down so that the cake is completely flat.

Use an offset spatula to evenly cover the cake with the rest of the frosting. It is meant to be a thin layer where you can still see the cake through the frosting. If you want a thicker coating, you will need to double the buttercream recipe.

For the top, drizzle more syrup and decorate with coffee truffles, shaved chocolate, or anything else your heart desires! Use a hot knife to cut the cake, wipe it clean in between slices, and enjoy!