To prepare the Limoncello syrup, simply dilute the liquor with the water and lemon juice. For the preparation of the Tiramisu cream; whip the fresh cream together with the icing sugar until stiff and thick. Gently fold in the mascarpone, followed by ½ the quantity of lemon curd and zest. Slice the cake into 1 cm thick slices. Dress the cake slices, one next to the other, neatly onto a serving plate, brush with the lemon syrup. Pipe over the lemon cake the mascarpone cream and drizzle with the lemon curd. Cover the layer of cream with another layer of cake and repeat process. Take any remaining slices or crumbs from the lemon cake and rub into fine cake crumbs, sprinkle on the top of the tiramisu. Chill for at least 2 hours before serving.