Beat the eggs with the sugar and salt until the mixture triples in volume and turns pale. Gently fold in the sifted flour and cocoa with a spatula. Divide the batter between 3 lined round pans, or bake in batches, at 350°F for about 10–12 minutes. Let cool completely.
Beat the mascarpone with the powdered sugar until smooth. Add the heavy whipping cream and whip until firm. Fold in the concentrated coffee at the end. Divide the cream in two for the filling and keep some in a piping bag for the top decoration.
Place the first sponge layer on a serving platter. Using a piping bag with a round tip, pipe a ring of cream “dots” around the edge of the cake layer, then fill the center with the remaining cream and smooth it lightly with a spatula. Place the second layer on top of the cream. Press gently, then repeat the same process: pipe the cream dots around the edge, then fill the center.
Place the final layer on top. Melt the chocolate with the heavy cream over low heat or in the microwave, stirring until smooth. Let it cool slightly, then spread it evenly over the top of the cake.
Finish by decorating the top with more cream dots around the edge, just like on the earlier layers.
Notes
Use very cold mascarpone and cream for the best texture.
Do not overmix the filling after adding the coffee.
Chill the cake before slicing for cleaner layers.
A piping bag makes assembly and decoration easier.
Coffee can be adjusted slightly to taste, but keep it concentrated.
For a more accessible version, cream cheese can replace mascarpone.