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

Sift together the cake flour, baking powder, and a pinch of salt in a mixing bowl.

Combine instant espresso powder with boiling water, stirring until dissolved, then let cool.

Beat softened unsalted butter until creamy, gradually add sugar, mixing until light and fluffy.

Add eggs one at a time, mixing well after each addition, then mix in vanilla extract.

Gradually alternate adding the dry ingredients and whole milk to the butter mixture, mixing just until combined.

Divide the prepared batter between the two cake pans and bake for 20 minutes.

Allow the cakes to cool in their pans for about 10 minutes, then transfer to a wire rack.

Whisk mascarpone cheese until creamy, then blend in powdered sugar and fold in heavy cream.

Slice each cooled cake layer horizontally to create two thinner layers, brush with liquor or coffee.

Layer frosting between each cake layer and spread a thick layer on the exterior of the cake.

Chill the assembled cake in refrigerator for at least 1 hour before serving.