1. Preheat the oven to 350°F (175°C). Grease and line three 8-inch round cake pans, or two 9-inch pans, with parchment on the bottom and lightly dust the sides with cocoa powder or flour.

2. In a large mixing bowl whisk together the all-purpose flour, granulated sugar, brown sugar, unsweetened cocoa powder, baking powder, baking soda, and fine sea salt until evenly combined with no visible cocoa streaks.

3. In a separate bowl whisk the eggs, vegetable oil, whole milk, sour cream, brewed espresso, and vanilla extract until smooth and well blended.

4. Pour the wet ingredients into the dry ingredients and mix on low speed or whisk gently just until the batter is combined, scraping the bottom and sides of the bowl so no dry pockets remain; the batter will be slightly thin.

5. Divide the batter evenly between the prepared cake pans and tap each pan lightly on the counter to release any large air bubbles.

6. Bake the cakes for 25–30 minutes, or until the centers spring back lightly when touched and a toothpick inserted into the middle comes out with just a few moist crumbs attached.

7. Let the cake layers cool in their pans for 10 minutes, then carefully invert onto a wire rack, peel off the parchment, and allow them to cool completely before frosting.

8. While the cakes cool, make the espresso buttercream by beating the softened unsalted butter in a large bowl on medium-high speed for 2–3 minutes until smooth and slightly lighter in color.

9. In a small bowl stir the espresso powder into 2 tablespoons of the heavy cream or milk until dissolved.

10. Gradually add the powdered sugar to the butter in 1-cup increments, mixing on low speed at first, then increasing to medium-high once the sugar begins to incorporate, scraping the bowl as needed.

11. Add the dissolved espresso mixture, remaining heavy cream or milk as needed, vanilla extract, and fine sea salt to the buttercream and beat on medium-high speed until the frosting is light, fluffy, and spreadable.

12. Level the cooled cake layers if domed, then place the first layer on a cake stand or serving plate and spread a generous layer of espresso buttercream over the top.

13. Add the second layer and repeat with more buttercream, then top with the final layer and use the remaining frosting to coat the sides and top of the cake, smoothing or swirling the buttercream to your desired finish.

14. Chill the frosted cake in the refrigerator for 20–30 minutes to help the buttercream firm up before adding the ganache drip.

15. To make the ganache, place the chopped dark chocolate in a heatproof bowl. Heat the heavy cream in a small saucepan over medium heat until steaming and just beginning to simmer around the edges, but not boiling.

16. Pour the hot cream over the chocolate and let it sit undisturbed for 1–2 minutes, then stir slowly from the center outward until the mixture is smooth and glossy.

17. Stir in the espresso powder if using, then let the ganache cool for 10–15 minutes until it thickens slightly but is still pourable and will gently drip down the sides of the cake.

18. Remove the chilled cake from the refrigerator and spoon or pour the ganache onto the center of the cake, nudging it toward the edges with an offset spatula or the back of a spoon so it drips down the sides in controlled streams.

19. While the ganache is still soft, decorate the top of the cake with chocolate shavings or curls and chocolate-covered espresso beans if desired.

20. Let the ganache set at room temperature for at least 20 minutes before slicing for the cleanest cuts, then serve and enjoy.