1. Preheat & Prepare Pans
Preheat your oven to 350°F (177°C). Grease two 9-inch round cake pans, line the bottoms with parchment paper rounds, then lightly grease the parchment. This helps the cakes release easily after baking.

2. Make the Cake Batter
In a large mixing bowl, whisk together the flour, cocoa powder, sugar, baking soda, baking powder, salt, and espresso powder (if using).
In a separate bowl, use a whisk or electric mixer to combine the oil, eggs, and vanilla until smooth. Mix in the buttermilk.
Pour the wet mixture into the dry ingredients, add the hot water or coffee, and mix on low speed (or whisk by hand) until the batter is fully blended. The batter will be thin.

3. Bake the Cakes
Divide the batter evenly between the prepared pans. Bake for 23–26 minutes, or until a toothpick inserted in the center comes out clean.
Note: The centers may slightly sink as they cool—this is normal due to the high moisture content and cocoa powder structure.

4. Cool Completely
Remove from the oven and let the cakes cool fully in their pans on a wire rack.

5. Make the Buttercream
Using a hand or stand mixer with a paddle attachment, beat the butter on medium speed until smooth and creamy (about 2 minutes).
Add the confectioners’ sugar, cocoa powder, 3 tablespoons of heavy cream, vanilla, and salt. Start on low speed, then beat on high for 1 minute until fluffy.
Adjust consistency if needed: add a bit more sugar or cocoa if too soft, or an extra tablespoon of cream if too stiff. Taste and add a pinch more salt if desired.

6. Assemble & Frost
If the cake layers have domed tops, trim them flat with a serrated knife.
Place the first layer on your serving plate and spread a generous amount of frosting on top. Add the second layer and frost the top and sides.
Use an icing spatula or bench scraper to smooth it out.

7. Chill Before Serving
Refrigerate the cake uncovered for at least 30–60 minutes to help it set before slicing. Serve chilled or at room temperature. The cake can be refrigerated for 4–6 hours ahead of time if needed.

8. Storage
Cover leftovers tightly and store in the fridge for up to 5 days. A cake carrier works great for storing and transporting.