Start by heating your oven to 350°F (175°C). Lightly grease two 8-inch cake pans, then line the bottoms with parchment paper to prevent sticking. Set the pans aside while you prepare the batter.

In a medium mixing bowl, combine the all-purpose flour, baking powder, and salt. Whisk everything together until the ingredients are evenly distributed.

Place the softened butter and granulated sugar in a large mixing bowl. Beat them together for about 3 to 4 minutes until the mixture becomes light in color and fluffy in texture.

Add the eggs one at a time, mixing well after each addition so they are fully incorporated. Pour in the vanilla extract and mix again until smooth.

Gradually add the flour mixture to the butter mixture in three portions, alternating with the milk or buttermilk. Start and finish with the dry ingredients. Mix gently after each addition, stopping as soon as the batter is smooth and combined.

Divide the batter evenly between the prepared cake pans and spread it into an even layer. Bake for 30 to 35 minutes, or until a toothpick inserted into the center comes out clean. Let the cakes cool in the pans for 10 minutes before transferring them to a wire rack to cool completely.

For the chocolate buttercream, beat the softened butter until creamy and smooth. Add the cocoa powder and espresso powder, mixing until combined. Gradually add the confectioners’ sugar, alternating with the milk or cream. Stir in the vanilla extract, then continue beating for 3 to 4 minutes until the frosting is light, smooth, and fluffy.

Place one cooled cake layer on a serving plate or cake stand. Spread a generous layer of chocolate buttercream over the top. Position the second cake layer on top and cover the top and sides of the cake with the remaining buttercream. Slice and serve.