1-Preheat oven: Preheat oven to 350°F and prepare three 6-inch layer cake pans by greasing them lightly.

2-Whisk dry ingredients: Whisk the dry ingredients together in a bowl: flour, cocoa powder, espresso powder, baking powder, salt, and optionally baking soda.

3-Whisk wet ingredients: In a separate bowl, whisk the wet ingredients: oil, sugar, eggs, milk, and vanilla extract.

4-Combine mixtures: Gradually combine the dry ingredients into the wet mixture, adding the ½ cup brewed espresso or coffee (mixed with milk if needed) in the middle. The batter will be thin, so mix gently.

5-Bake layers: Divide the batter equally among the pans and bake for 25-30 minutes, or until a tester comes out clean. Let the layers cool completely and trim them even for assembly.

6-Make buttercream: For the buttercream, brown the unsalted butter and let it cool, then cream it until smooth. Gradually beat in the powdered sugar, and add vanilla extract, salt, espresso powder, and heavy cream. Beat on high until fluffy.

7-Assemble cake: To assemble, layer the cakes with ¼ of the buttercream between each layer, placing the top layer upside down. Apply a thin crumb coat and chill for 30-60 minutes, then frost smoothly with the remaining buttercream and chill for another 20-30 minutes.

8-Prepare ganache and decorate: For the ganache, heat the heavy cream until hot but not boiling, pour it over the chopped dark chocolate, let it sit for 2 minutes, and stir until smooth. Cool slightly, then pour over the chilled cake top for a drip effect. Chill for 10-15 minutes to set, and optionally decorate with piped buttercream dollops and chocolate shavings.