For the buttercreams, place the egg yolks in the bowl of a heavy-duty mixer fitted with the whip and whisk in the sugar. Whisk in the brandy; then place the bowl over a pan of simmering water, whisking constantly, until the mixture thickens slightly. Return the bowl to the mixer and whip on medium speed until cold and increased in volume. Beat in the butter in 5 or 6 additions and continue beating until the mixture is smooth and light.
To flavor, cut the chocolate finely. Bring the water to a boil and remove from the heat. Add the chocolate and stir to melt. Cool. Then combine the instant espresso powder and water and stir to dissolve. Divide the buttercream in half and beat the cooled chocolate mixture into one half and the coffee into the other.
To assemble the cake, cut two ¼-inch slices from the layer, using a long, serrated knife. Place one slice on a cardboard cake circle and reserve the other one, covered with plastic wrap. Cut the remainder of the cake into 3 layers, then trim one to a 9-inch-round layer, the second to an 8-inch-round layer, and the third to a 7-inch-round layer. Reserve the scraps, covered with plastic wrap.
Moisten the layer on the cardboard lightly with the Marsala, then spread with one-fourth of the coffee buttercream. Place the 9-inch-round layer on the cream and moisten with the Marsala. Spread with one-fourth of the chocolate butter-cream. Place the 8-inch-round layer on the cream, moisten with the Marsala, and spread with another fourth of the coffee cream. Place the 7-inch-round layer on top and moisten. Spread with another fourth of the chocolate cream. Use the scraps to form a rough 6-inch-round layer on the cream. Moisten and spread with another fourth of the coffee cream. Use more scraps to form a 5-inch-round layer, then moisten and spread with another fourth of the chocolate cream. Use the last scraps to form a 4-inch-round layer. Moisten it and spread the entire outside of the cake with the remaining coffee cream. Make a cut in the reserved layer, from the center outward to the edge, and arrange it on the stacked dome of layers, smoothly, overlapping it at the cut. Moisten with the last Marsala and spread with the remaining chocolate cream. Crush the amaretti coarsely and press them all over the outside of the cake. Chill the cake so that the filling sets. Dust lightly with the confectioners’ sugar just before serving.