Preheat your oven to 350°F (177°C). Grease and line two 6-inch round cake pans with parchment paper.

In a medium mixing bowl, sift together the cake flour, baking powder, and salt.

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

In a stand mixer, beat the softened unsalted butter until fluffy, then gradually add sugar and mix until light and creamy.

Add vanilla extract and eggs, one at a time, mixing well after each addition.

Gradually add the dry mixture along with whole milk, mixing until just combined, then fold in the cooled espresso.

Divide the batter evenly between the prepared cake pans. Bake for about 20 minutes until a toothpick comes out with a few moist crumbs.

Allow the cakes to cool in the pans for 10 minutes, then transfer to wire racks to cool completely.

In a large mixing bowl, whisk the mascarpone cheese until creamy, blend in powdered sugar, chilled coffee, and heavy cream until smooth.

Slice each cake layer horizontally to create four layers. Soak each layer with coffee or liquor, frost between layers and cover the entire cake with frosting.

Dust the top of the cake with cocoa powder for finishing.

Let set at room temperature for about 20 minutes before slicing and serving.