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.

Cut a piece of cardboard to fit inside the base of a 24cm x 13cm x 6.5cm loaf pan. Wrap the cardboard in aluminium foil (this provides a stable base to help remove tiramisu once set). Grease the pan and line base and long sides with a double layer of baking paper with a 5cm overhang. (Grease in between baking paper layers to stick them together.) Place the aluminium-covered cardboard over the baking paper in the base of the pan. Measure savoiardi against the pan, trimming to fit if necessary.

In a stand mixer fitted with the whisk attachment, whisk yolks and sugar on high speed for 3 minutes, or until thick and pale and sugar has partially dissolved. Whisk in remaining ½ cup (125ml) cream and vanilla until smooth and thickened and sugar has completely dissolved. Reduce speed to low and whisk in mascarpone and lemon curd until combined and thick (when you lift the whisk from the mixture, the cream should fall back in thick trails that remain). Whisk in the cooled cream and gelatine mix until combined. Set aside.

Place limoncello in a wide bowl. Working with 1 biscuit at a time, dip both sides of biscuit in limoncello and place in prepared pan to line base. Repeat to form 2 layers of biscuits. Slightly press down on biscuits. Top with half of the cream mixture. Continue with another layer of dipped biscuits and remaining cream mixture. Dip remaining biscuits in limoncello and arrange on top. Cover with plastic wrap and 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.