Start by preheating your oven to 350°F (175°C) and preparing two 8-inch cake pans by lining them with parchment paper and lightly greasing the sides.

In a small heatproof bowl, whisk together the Dutch-process cocoa powder and instant espresso powder. Carefully pour in the boiling water and whisk until the mixture becomes smooth and glossy. Set it aside and let it cool completely so it doesn’t affect the batter later.

In a large mixing bowl, whisk together the flour, salt, baking soda, and brown sugar. Break up any sugar lumps with your hands or whisk so everything is evenly mixed.

In another bowl, combine the sour cream (or yogurt), eggs, oil, and vanilla extract. Whisk until smooth and fully blended.

Now pour the wet mixture into the dry ingredients. Start mixing slowly from the center and gently combine until mostly mixed. Then add the cooled cocoa mixture and stir until the batter becomes smooth and fully combined. Don’t overmix—just mix until everything is incorporated.

Bake the cake

Divide the batter evenly between the prepared cake pans. Tap each pan lightly on the counter a few times to release any trapped air bubbles.

Place the pans in the oven and bake for 32–35 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs.

Once baked, remove the cakes from the oven and let them cool in the pans for about 30 minutes. Then carefully run a knife around the edges and transfer them to a wire rack to cool completely. Make sure the cakes are fully cooled before frosting.

In a small saucepan, heat the heavy cream until it just begins to simmer—don’t let it boil. Remove from heat and pour it over the chopped semisweet chocolate. Let it sit for 2–3 minutes, then stir until smooth and glossy. Set aside and allow it to cool until slightly thickened but still soft.

In a large mixing bowl, beat the room-temperature butter on medium speed until creamy and smooth. Add powdered sugar, sifted cocoa powder, vanilla extract, and salt. Mix on low speed first, then increase speed and beat until fluffy.

Slowly pour in the cooled chocolate ganache and continue beating for 2–3 minutes until the frosting becomes light, creamy, and spreadable.

If needed, level the tops of the cake layers using a serrated knife to create flat surfaces.

Place one cake layer on your serving plate or cake stand. Spread an even layer of frosting on top, making sure it reaches the edges. Place the second layer on top, preferably upside down for a smooth finish.

Now spread the remaining frosting over the top and sides of the cake. Use an offset spatula to smooth it out for a clean, bakery-style look.

Slice and serve. For best results, let the cake sit at room temperature for 20–30 minutes before serving so the frosting softens slightly and the flavors fully develop.