Line a 1.2-litre pudding basin with cling wrap, leaving enough hanging over the edges to fold over the top of the pudding and cover securely.
Slice the cake horizontally into 3 layers, set aside 1 layer and then cut both of the remaining layers into 8 triangular slices.
Line the pudding basin with the cake slices, the pointed ends at the bottom of the basin.
Patch any holes with spare pieces of cake (you may not need all the slices) so the whole basin is lined with cake.
Use a pastry brush to brush the cake with 2 tablespoons of the amaretto.
Whip the cream until soft peaks form.
Place the ricotta, mascarpone, lemon zest and icing sugar in a food processor and process until smooth.
Add the ricotta mixture to the cream and stir in 1 tablespoon amaretto.
Transfer half the mixture to another bowl and stir in the almonds, mixed peel and half of the dark chocolate, set aside.
Melt the chocolate over simmering water or using the method you prefer, stirring occasionally and when melted, remove from heat and cool slightly.
Stir this into the other half of the ricotta mixture.
Sift in the cocoa powder, stir until smooth and allow to cool completely.
Spread the melted chocolate and ricotta mixture over the sides of the sponge cake in a thick layer and fill the center with the almond and ricotta mixture.
Cover this with the reserved round of sponge, trimming the edges to fit the basin.
Brush the top with the remaining tablespoon of amaretto. Fold over the plastic wrap and cover tightly, weigh down and refrigerate overnight.
When it’s ready to serve, turn out the zuccotto carefully onto a plate.
Cut out 2 triangular templates from baking paper and dust the zuccotto with alternate triangles of cocoa powder and icing sugar, covering the dusted areas with the template as you go.
Serve zuccotto in slices.