Preheat your oven to 350°F (177°C) and grease two 6-inch round cake pans.

Sift together cake flour, baking powder, and salt in a medium mixing bowl.

Dissolve the instant espresso powder in boiling water and allow to cool.

Beat unsalted butter until creamy, then gradually add granulated sugar, mixing until fluffy in a large bowl.

Combine sifted dry ingredients and milk with the butter mixture; fold in cooled espresso mixture.

Divide batter into prepared pans and bake for approximately 20 minutes.

Let cakes cool in pans for 5 minutes, then invert on a wire rack to cool completely.

Whisk mascarpone cheese, fold in sifted powdered sugar and espresso; then add heavy whipping cream until fluffy.

Slice each cooled cake layer in half horizontally for four layers. Brush with liquor or coffee.

Assemble and frost layers generously with mascarpone frosting, then cover the entire cake.

Dust the top with cocoa powder, chill for at least 30 minutes before serving.