Preheat the oven to 180°C and line a 35x25cm tin with parchment.
Whisk eggs and caster sugar for five minutes until pale and thick.
Gently fold in the sifted flour using a metal spoon.
Pour the batter into the tin and level the surface.
Bake for 20 minutes until golden and then cool completely on a rack.
Dissolve coffee in boiling water and stir in the brandy.
Slice the cooled sponge horizontally into two thin layers.
Cut two 18cm squares from each sponge layer.
Line an 18cm square tin with parchment paper overlapping the sides.
Beat mascarpone until smooth then whisk in cream and icing sugar.
Layer one sponge in the tin, soak with coffee mixture, then top with frosting and chocolate.
Repeat the layering process for the second and third sponges.
Add the final sponge, soak, and apply a thin crumb coat of frosting.
Spread the remaining frosting on top and chill for one hour.
Melt half the chopped chocolate over a water bath until it reaches 53°C.
Stir in remaining chocolate until it cools to 31°C.
Prepare a paper piping bag with the tempered chocolate.
Pipe decorative shapes onto parchment and allow them to set.
Dust with cocoa powder, remove from the tin, and decorate with chocolate shapes.