Prepare Coffee Simple Syrup by combining equal parts water and sugar with espresso powder over medium heat. Stir until dissolved and simmer for 3–5 minutes. Remove from heat and cool for 15 minutes.

Preheat oven to 350°F (175°C). Whisk flour, baking powder, and salt in one bowl. In another, cream butter and sugar until fluffy. Add eggs one at a time, then alternate dry ingredients with buttermilk. Pour into greased pans and bake for 30-35 minutes.

Let cakes cool in pans for 10 minutes, then invert onto a wire rack to cool completely.

Beat softened butter with mascarpone until light and fluffy. Gradually add powdered sugar until smooth, then add vanilla extract.

Slice each cooled cake layer in half horizontally. Soak each layer with coffee syrup and spread frosting between layers.

Apply a crumb coat of frosting around the cake and chill for 30 minutes. Then frost smoothly and decorate with sifted cocoa powder or chocolate shavings.

Chill the cake in the refrigerator for at least 2 hours before serving for the best flavor.