Place ½ cup (125ml) cream in a small saucepan and bring to just below the boil. Remove from the heat. Squeeze excess water from gelatine and stir into hot cream until dissolved. Set aside and cool to room temperature.

Place yolks and sugar in the bowl of a stand mixer with the whisk attachment and whisk for 5 minutes on high speed until thick and pale and sugar has partially dissolved. Whisk in remaining 400ml cream and vanilla until stiff peaks form (about 5 mins) and sugar has completely dissolved. reduce speed to low and whisk in mascarpone and lemon curd until combined and thick. Whisk in cooled cream and gelatine mix. Set aside.

Cut a piece of cardboard to fit inside a 2.7L 24cm x 10cm x 11cm terrine mould. Wrap the cardboard in aluminium foil (this provides a stable base to help remove tiramisu once set. Grease the mould and line base and long sides with a double layer of baking paper with 5cm overhang. (Grease in between layers to stick them together).

Place the aluminium-covered cardboard over the baking paper in the base of the pan. Measure savoiardi against the mould, trimming to fit if necessary.

Place limoncello in a wide bowl. Dip both sides of 8 savoiardi biscuits in limoncello and place in mould, then dip another 8 and lay on top to create a 2-layer biscuit base. Top with half of the cream mixture. Continue layering with 8 dipped biscuits and remaining cream mixture. Dip remaining 8 biscuits in limoncello, arrange on top. Chill overnight or until set. Using overhanging baking paper, lift tiramisu from mould and transfer to a serving plate.

Dust with icing sugar to serve.