For the sponge cake, preheat oven to 180˚C.
Butter and flour a 23 cm spring-form pan.
Put the eggs into the bowl of a mixer and beat for five minutes.
Add the sugar and grated peel and continue to beat until the mixture forms a ribbon when poured, about 15 minutes.
In two or three parts, gently fold in the sifted flour.
Pour into the spring-form pan and bake for 25 to 30 minutes, or until a need inserted into the center of the cake comes out clean.
Cool on a cake rack. Set it aside.
Cut the marzipan log lengthwise into 1,25 cm-thick slices.
Roll out three of the slices into strips about 3 to 6 mm thick.
Knead the remaining marzipan into a ball, wrap it in plastic, and store in the refrigerator for later use.
Line a 23 cm cassata pan, or a 23 cm pie pan with sloping sides, with plastic wrap.
Line the sides of the pan with the marzipan strips, slightly overlapping the ends.
Press against the pan to form a smooth layer.
For the syrup, Pour the water into a small bowl, add the sugar and Grand Marnier.
Stir to dissolve the sugar.
Cut the cake from top to bottom into ½ in thick slices and trim the crust.
Put a layer of slices on the bottom of the pan.
Spoon 4 to 5 tablespoons of sugar on top.
Spread evenly with the ricotta cream.
Carefully place another layer of cake slices on top.
Add the rest of the syrup.
Remove the outer plastic wrap from the cassata pan and invert it onto a serving plate.
Carefully lift off the pan and peel off the remaining plastic.
Set the cassata aside while you are making the icing.
Sift half of the confectioner’s sugar into a bowl.
Add half of the lemon juice and all of the lemon extract.
Stir the liquid into the sugar, braking up any lumps.
Sift the remaining sugar into the bowl and add the rest of the lemon juice.
Thin the icing with a little water, if necessary, until it has a thin spreading consistency and forms a smooth, shiny icing.
Ice the top of the cassata, leaving the marzipan sides of the cake visible.
If you are not using green marzipan, ice the entire cake.
Decorate with whole and cut candied fruit. Refrigerate and allow to set for at least 1 to 2 hours before serving.